Minimal refactor of existing random API, move samplers implementations to samplers package, implement Sampler<T> by all the Samplers

kmath-coroutines/src/commonMain/kotlin/scientifik/kmath/chains/Chain.kt

@@ -19,6 +19,7 @@ package scientifik.kmath.chains
 import kotlinx.coroutines.InternalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.FlowCollector
+import kotlinx.coroutines.flow.flow
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 
@@ -27,7 +28,7 @@ import kotlinx.coroutines.sync.withLock
  * A not-necessary-Markov chain of some type
  * @param R - the chain element type
  */
-interface Chain<out R>: Flow<R> {
+interface Chain<out R> : Flow<R> {
     /**
      * Generate next value, changing state if needed
      */
@@ -39,13 +40,11 @@ interface Chain<out R>: Flow<R> {
     fun fork(): Chain<R>
 
     @OptIn(InternalCoroutinesApi::class)
-    override suspend fun collect(collector: FlowCollector<R>) {
-        kotlinx.coroutines.flow.flow {
-            while (true){
+    override suspend fun collect(collector: FlowCollector<R>): Unit = flow {
+        while (true)
             emit(next())
-            }
+
     }.collect(collector)
-    }
 
     companion object
 }
@@ -66,24 +65,18 @@ class SimpleChain<out R>(private val gen: suspend () -> R) : Chain<R> {
  * A stateless Markov chain
  */
 class MarkovChain<out R : Any>(private val seed: suspend () -> R, private val gen: suspend (R) -> R) : Chain<R> {
-
-    private val mutex = Mutex()
-
+    private val mutex: Mutex = Mutex()
     private var value: R? = null
 
     fun value() = value
 
-    override suspend fun next(): R {
-        mutex.withLock {
+    override suspend fun next(): R = mutex.withLock {
         val newValue = gen(value ?: seed())
         value = newValue
         return newValue
     }
-    }
 
-    override fun fork(): Chain<R> {
-        return MarkovChain(seed = { value ?: seed() }, gen = gen)
-    }
+    override fun fork(): Chain<R> = MarkovChain(seed = { value ?: seed() }, gen = gen)
 }
 
 /**
@@ -97,24 +90,18 @@ class StatefulChain<S, out R>(
     private val forkState: ((S) -> S),
     private val gen: suspend S.(R) -> R
 ) : Chain<R> {
-
     private val mutex = Mutex()
-
     private var value: R? = null
 
     fun value() = value
 
-    override suspend fun next(): R {
-        mutex.withLock {
+    override suspend fun next(): R = mutex.withLock {
         val newValue = state.gen(value ?: state.seed())
         value = newValue
         return newValue
     }
-    }
 
-    override fun fork(): Chain<R> {
-        return StatefulChain(forkState(state), seed, forkState, gen)
-    }
+    override fun fork(): Chain<R> = StatefulChain(forkState(state), seed, forkState, gen)
 }
 
 /**
@@ -123,9 +110,7 @@ class StatefulChain<S, out R>(
 class ConstantChain<out T>(val value: T) : Chain<T> {
     override suspend fun next(): T = value
 
-    override fun fork(): Chain<T> {
-        return this
-    }
+    override fun fork(): Chain<T> = this
 }
 
 /**
@@ -143,9 +128,8 @@ fun <T, R> Chain<T>.map(func: suspend (T) -> R): Chain<R> = object : Chain<R> {
 fun <T> Chain<T>.filter(block: (T) -> Boolean): Chain<T> = object : Chain<T> {
     override suspend fun next(): T {
         var next: T
-        do {
-            next = this@filter.next()
-        } while (!block(next))
+        do next = this@filter.next()
+        while (!block(next))
         return next
     }
 
@@ -163,7 +147,9 @@ fun <T, R> Chain<T>.collect(mapper: suspend (Chain<T>) -> R): Chain<R> = object
 fun <T, S, R> Chain<T>.collectWithState(state: S, stateFork: (S) -> S, mapper: suspend S.(Chain<T>) -> R): Chain<R> =
     object : Chain<R> {
         override suspend fun next(): R = state.mapper(this@collectWithState)
-        override fun fork(): Chain<R> = this@collectWithState.fork().collectWithState(stateFork(state), stateFork, mapper)
+
+        override fun fork(): Chain<R> =
+            this@collectWithState.fork().collectWithState(stateFork(state), stateFork, mapper)
     }
 
 /**
@@ -171,6 +157,5 @@ fun <T, S, R> Chain<T>.collectWithState(state: S, stateFork: (S) -> S, mapper: s
  */
 fun <T, U, R> Chain<T>.zip(other: Chain<U>, block: suspend (T, U) -> R): Chain<R> = object : Chain<R> {
     override suspend fun next(): R = block(this@zip.next(), other.next())
-
     override fun fork(): Chain<R> = this@zip.fork().zip(other.fork(), block)
 }

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/UniformRandomProvider.kt

@@ -1,19 +0,0 @@
-package scientifik.kmath.commons.rng
-
-interface UniformRandomProvider {
-    fun nextBytes(bytes: ByteArray)
-
-    fun nextBytes(
-        bytes: ByteArray,
-        start: Int,
-        len: Int
-    )
-
-    fun nextInt(): Int
-    fun nextInt(n: Int): Int
-    fun nextLong(): Long
-    fun nextLong(n: Long): Long
-    fun nextBoolean(): Boolean
-    fun nextFloat(): Float
-    fun nextDouble(): Double
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/SharedStateSampler.kt

@@ -1,7 +0,0 @@
-package scientifik.kmath.commons.rng.sampling
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-
-interface SharedStateSampler<R> {
-    fun withUniformRandomProvider(rng: UniformRandomProvider): R
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/AhrensDieterExponentialSampler.kt

@@ -1,101 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-import kotlin.math.ln
-import kotlin.math.pow
-
-class AhrensDieterExponentialSampler : SamplerBase,
-    SharedStateContinuousSampler {
-    private val mean: Double
-    private val rng: UniformRandomProvider
-
-    constructor(
-        rng: UniformRandomProvider,
-        mean: Double
-    ) : super(null) {
-        require(mean > 0) { "mean is not strictly positive: $mean" }
-        this.rng = rng
-        this.mean = mean
-    }
-
-    private constructor(
-        rng: UniformRandomProvider,
-        source: AhrensDieterExponentialSampler
-    ) : super(null) {
-        this.rng = rng
-        mean = source.mean
-    }
-
-    override fun sample(): Double {
-        // Step 1:
-        var a = 0.0
-        var u: Double = rng.nextDouble()
-
-        // Step 2 and 3:
-        while (u < 0.5) {
-            a += EXPONENTIAL_SA_QI.get(
-                0
-            )
-            u *= 2.0
-        }
-
-        // Step 4 (now u >= 0.5):
-        u += u - 1
-
-        // Step 5:
-        if (u <= EXPONENTIAL_SA_QI.get(
-                0
-            )
-        ) {
-            return mean * (a + u)
-        }
-
-        // Step 6:
-        var i = 0 // Should be 1, be we iterate before it in while using 0.
-        var u2: Double = rng.nextDouble()
-        var umin = u2
-
-        // Step 7 and 8:
-        do {
-            ++i
-            u2 = rng.nextDouble()
-            if (u2 < umin) umin = u2
-            // Step 8:
-        } while (u > EXPONENTIAL_SA_QI[i]) // Ensured to exit since EXPONENTIAL_SA_QI[MAX] = 1.
-        return mean * (a + umin * EXPONENTIAL_SA_QI[0])
-    }
-
-    override fun toString(): String = "Ahrens-Dieter Exponential deviate [$rng]"
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateContinuousSampler =
-        AhrensDieterExponentialSampler(rng, this)
-
-    companion object {
-        private val EXPONENTIAL_SA_QI = DoubleArray(16)
-
-        fun of(
-            rng: UniformRandomProvider,
-            mean: Double
-        ): SharedStateContinuousSampler =
-            AhrensDieterExponentialSampler(
-                rng,
-                mean
-            )
-
-        init {
-            /**
-             * Filling EXPONENTIAL_SA_QI table.
-             * Note that we don't want qi = 0 in the table.
-             */
-            val ln2 = ln(2.0)
-            var qi = 0.0
-
-            EXPONENTIAL_SA_QI.indices.forEach { i ->
-                qi += ln2.pow(i + 1.0) / InternalUtils.factorial(
-                    i + 1
-                )
-                EXPONENTIAL_SA_QI[i] = qi
-            }
-        }
-    }
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/BoxMullerNormalizedGaussianSampler.kt

@@ -1,50 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-import kotlin.math.*
-
-class BoxMullerNormalizedGaussianSampler(
-    private val rng: UniformRandomProvider
-) :
-    NormalizedGaussianSampler,
-    SharedStateContinuousSampler {
-    private var nextGaussian: Double = Double.NaN
-
-    override fun sample(): Double {
-        val random: Double
-
-        if (nextGaussian.isNaN()) {
-            // Generate a pair of Gaussian numbers.
-            val x = rng.nextDouble()
-            val y = rng.nextDouble()
-            val alpha = 2 * PI * x
-            val r = sqrt(-2 * ln(y))
-
-            // Return the first element of the generated pair.
-            random = r * cos(alpha)
-
-            // Keep second element of the pair for next invocation.
-            nextGaussian = r * sin(alpha)
-        } else {
-            // Use the second element of the pair (generated at the
-            // previous invocation).
-            random = nextGaussian
-
-            // Both elements of the pair have been used.
-            nextGaussian = Double.NaN
-        }
-
-        return random
-    }
-
-    override fun toString(): String = "Box-Muller normalized Gaussian deviate [$rng]"
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateContinuousSampler =
-        BoxMullerNormalizedGaussianSampler(rng)
-
-    companion object {
-        @Suppress("UNCHECKED_CAST")
-        fun <S> of(rng: UniformRandomProvider): S where S : NormalizedGaussianSampler?, S : SharedStateContinuousSampler? =
-            BoxMullerNormalizedGaussianSampler(rng) as S
-    }
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/ContinuousSampler.kt

@@ -1,5 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-interface ContinuousSampler {
-    fun sample(): Double
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/DiscreteSampler.kt

@@ -1,5 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-interface DiscreteSampler {
-    fun sample(): Int
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/GaussianSampler.kt

@@ -1,55 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-
-class GaussianSampler :
-    SharedStateContinuousSampler {
-    private val mean: Double
-    private val standardDeviation: Double
-    private val normalized: NormalizedGaussianSampler
-
-    constructor(
-        normalized: NormalizedGaussianSampler,
-        mean: Double,
-        standardDeviation: Double
-    ) {
-        require(standardDeviation > 0) { "standard deviation is not strictly positive: $standardDeviation" }
-        this.normalized = normalized
-        this.mean = mean
-        this.standardDeviation = standardDeviation
-    }
-
-    private constructor(
-        rng: UniformRandomProvider,
-        source: GaussianSampler
-    ) {
-        mean = source.mean
-        standardDeviation = source.standardDeviation
-        normalized =
-            InternalUtils.newNormalizedGaussianSampler(
-                source.normalized,
-                rng
-            )
-    }
-
-    override fun sample(): Double = standardDeviation * normalized.sample() + mean
-
-    override fun toString(): String = "Gaussian deviate [$normalized]"
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateContinuousSampler {
-        return GaussianSampler(rng, this)
-    }
-
-    companion object {
-        fun of(
-            normalized: NormalizedGaussianSampler,
-            mean: Double,
-            standardDeviation: Double
-        ): SharedStateContinuousSampler =
-            GaussianSampler(
-                normalized,
-                mean,
-                standardDeviation
-            )
-    }
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/LargenMeanPoissonSampler.kt

@@ -1,251 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-import kotlin.math.*
-
-class LargeMeanPoissonSampler :
-    SharedStateDiscreteSampler {
-    private val rng: UniformRandomProvider
-    private val exponential: SharedStateContinuousSampler
-    private val gaussian: SharedStateContinuousSampler
-    private val factorialLog: InternalUtils.FactorialLog
-    private val lambda: Double
-    private val logLambda: Double
-    private val logLambdaFactorial: Double
-    private val delta: Double
-    private val halfDelta: Double
-    private val twolpd: Double
-    private val p1: Double
-    private val p2: Double
-    private val c1: Double
-    private val smallMeanPoissonSampler: SharedStateDiscreteSampler
-
-    constructor(
-        rng: UniformRandomProvider,
-        mean: Double
-    ) {
-        require(mean >= 1) { "mean is not >= 1: $mean" }
-        // The algorithm is not valid if Math.floor(mean) is not an integer.
-        require(mean <= MAX_MEAN) { "mean $mean > $MAX_MEAN" }
-        this.rng = rng
-        gaussian =
-            ZigguratNormalizedGaussianSampler(rng)
-        exponential =
-            AhrensDieterExponentialSampler.of(
-                rng,
-                1.0
-            )
-        // Plain constructor uses the uncached function.
-        factorialLog = NO_CACHE_FACTORIAL_LOG!!
-        // Cache values used in the algorithm
-        lambda = floor(mean)
-        logLambda = ln(lambda)
-        logLambdaFactorial = getFactorialLog(lambda.toInt())
-        delta = sqrt(lambda * ln(32 * lambda / PI + 1))
-        halfDelta = delta / 2
-        twolpd = 2 * lambda + delta
-        c1 = 1 / (8 * lambda)
-        val a1: Double = sqrt(PI * twolpd) * exp(c1)
-        val a2: Double = twolpd / delta * exp(-delta * (1 + delta) / twolpd)
-        val aSum = a1 + a2 + 1
-        p1 = a1 / aSum
-        p2 = a2 / aSum
-
-        // The algorithm requires a Poisson sample from the remaining lambda fraction.
-        val lambdaFractional = mean - lambda
-        smallMeanPoissonSampler =
-            if (lambdaFractional < Double.MIN_VALUE) NO_SMALL_MEAN_POISSON_SAMPLER else  // Not used.
-                KempSmallMeanPoissonSampler.of(
-                    rng,
-                    lambdaFractional
-                )
-    }
-
-    internal constructor(
-        rng: UniformRandomProvider,
-        state: LargeMeanPoissonSamplerState,
-        lambdaFractional: Double
-    ) {
-        require(!(lambdaFractional < 0 || lambdaFractional >= 1)) { "lambdaFractional must be in the range 0 (inclusive) to 1 (exclusive): $lambdaFractional" }
-        this.rng = rng
-        gaussian =
-            ZigguratNormalizedGaussianSampler(rng)
-        exponential =
-            AhrensDieterExponentialSampler.of(
-                rng,
-                1.0
-            )
-        // Plain constructor uses the uncached function.
-        factorialLog = NO_CACHE_FACTORIAL_LOG!!
-        // Use the state to initialise the algorithm
-        lambda = state.lambdaRaw
-        logLambda = state.logLambda
-        logLambdaFactorial = state.logLambdaFactorial
-        delta = state.delta
-        halfDelta = state.halfDelta
-        twolpd = state.twolpd
-        p1 = state.p1
-        p2 = state.p2
-        c1 = state.c1
-
-        // The algorithm requires a Poisson sample from the remaining lambda fraction.
-        smallMeanPoissonSampler =
-            if (lambdaFractional < Double.MIN_VALUE)
-                NO_SMALL_MEAN_POISSON_SAMPLER
-            else  // Not used.
-                KempSmallMeanPoissonSampler.of(
-                    rng,
-                    lambdaFractional
-                )
-    }
-
-    /**
-     * @param rng Generator of uniformly distributed random numbers.
-     * @param source Source to copy.
-     */
-    private constructor(
-        rng: UniformRandomProvider,
-        source: LargeMeanPoissonSampler
-    ) {
-        this.rng = rng
-        gaussian = source.gaussian.withUniformRandomProvider(rng)!!
-        exponential = source.exponential.withUniformRandomProvider(rng)!!
-        // Reuse the cache
-        factorialLog = source.factorialLog
-        lambda = source.lambda
-        logLambda = source.logLambda
-        logLambdaFactorial = source.logLambdaFactorial
-        delta = source.delta
-        halfDelta = source.halfDelta
-        twolpd = source.twolpd
-        p1 = source.p1
-        p2 = source.p2
-        c1 = source.c1
-
-        // Share the state of the small sampler
-        smallMeanPoissonSampler = source.smallMeanPoissonSampler.withUniformRandomProvider(rng)!!
-    }
-
-    /** {@inheritDoc}  */
-    override fun sample(): Int {
-        // This will never be null. It may be a no-op delegate that returns zero.
-        val y2: Int = smallMeanPoissonSampler.sample()
-        var x: Double
-        var y: Double
-        var v: Double
-        var a: Int
-        var t: Double
-        var qr: Double
-        var qa: Double
-        while (true) {
-            // Step 1:
-            val u = rng.nextDouble()
-
-            if (u <= p1) {
-                // Step 2:
-                val n = gaussian.sample()
-                x = n * sqrt(lambda + halfDelta) - 0.5
-                if (x > delta || x < -lambda) continue
-                y = if (x < 0) floor(x) else ceil(x)
-                val e = exponential.sample()
-                v = -e - 0.5 * n * n + c1
-            } else {
-                // Step 3:
-                if (u > p1 + p2) {
-                    y = lambda
-                    break
-                }
-
-                x = delta + twolpd / delta * exponential.sample()
-                y = ceil(x)
-                v = -exponential.sample() - delta * (x + 1) / twolpd
-            }
-            // The Squeeze Principle
-            // Step 4.1:
-            a = if (x < 0) 1 else 0
-            t = y * (y + 1) / (2 * lambda)
-
-            // Step 4.2
-            if (v < -t && a == 0) {
-                y += lambda
-                break
-            }
-
-            // Step 4.3:
-            qr = t * ((2 * y + 1) / (6 * lambda) - 1)
-            qa = qr - t * t / (3 * (lambda + a * (y + 1)))
-
-            // Step 4.4:
-            if (v < qa) {
-                y += lambda
-                break
-            }
-
-            // Step 4.5:
-            if (v > qr) continue
-
-            // Step 4.6:
-            if (v < y * logLambda - getFactorialLog((y + lambda).toInt()) + logLambdaFactorial) {
-                y += lambda
-                break
-            }
-        }
-
-        return min(y2 + y.toLong(), Int.MAX_VALUE.toLong()).toInt()
-    }
-
-
-    private fun getFactorialLog(n: Int): Double = factorialLog.value(n)
-
-    override fun toString(): String = "Large Mean Poisson deviate [$rng]"
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateDiscreteSampler =
-        LargeMeanPoissonSampler(rng, this)
-
-    val state: LargeMeanPoissonSamplerState
-        get() = LargeMeanPoissonSamplerState(
-            lambda, logLambda, logLambdaFactorial,
-            delta, halfDelta, twolpd, p1, p2, c1
-        )
-
-    class LargeMeanPoissonSamplerState(
-        val lambdaRaw: Double,
-        val logLambda: Double,
-        val logLambdaFactorial: Double,
-        val delta: Double,
-        val halfDelta: Double,
-        val twolpd: Double,
-        val p1: Double,
-        val p2: Double,
-        val c1: Double
-    ) {
-        fun getLambda(): Int = lambdaRaw.toInt()
-    }
-
-    companion object {
-        private const val MAX_MEAN = 0.5 * Int.MAX_VALUE
-        private var NO_CACHE_FACTORIAL_LOG: InternalUtils.FactorialLog? = null
-
-        private val NO_SMALL_MEAN_POISSON_SAMPLER: SharedStateDiscreteSampler =
-            object : SharedStateDiscreteSampler {
-                override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateDiscreteSampler =
-// No requirement for RNG
-                    this
-
-                override fun sample(): Int =// No Poisson sample
-                    0
-            }
-
-        fun of(
-            rng: UniformRandomProvider,
-            mean: Double
-        ): SharedStateDiscreteSampler =
-            LargeMeanPoissonSampler(rng, mean)
-
-        init {
-            // Create without a cache.
-            NO_CACHE_FACTORIAL_LOG =
-                InternalUtils.FactorialLog.create()
-        }
-    }
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/NormalizedGaussianSampler.kt

@@ -1,4 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-interface NormalizedGaussianSampler :
-    ContinuousSampler

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/PoissonSampler.kt

@@ -1,40 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-
-class PoissonSampler(
-    rng: UniformRandomProvider,
-    mean: Double
-) : SamplerBase(null),
-    SharedStateDiscreteSampler {
-    private val poissonSamplerDelegate: SharedStateDiscreteSampler
-
-    override fun sample(): Int = poissonSamplerDelegate.sample()
-    override fun toString(): String = poissonSamplerDelegate.toString()
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateDiscreteSampler? =
-// Direct return of the optimised sampler
-        poissonSamplerDelegate.withUniformRandomProvider(rng)
-
-    companion object {
-        const val PIVOT = 40.0
-
-        fun of(
-            rng: UniformRandomProvider,
-            mean: Double
-        ): SharedStateDiscreteSampler =// Each sampler should check the input arguments.
-            if (mean < PIVOT) SmallMeanPoissonSampler.of(
-                rng,
-                mean
-            ) else LargeMeanPoissonSampler.of(
-                rng,
-                mean
-            )
-    }
-
-    init {
-        // Delegate all work to specialised samplers.
-        poissonSamplerDelegate =
-            of(rng, mean)
-    }
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/SamplerBase.kt

@@ -1,12 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-
-@Deprecated("Since version 1.1. Class intended for internal use only.")
-open class SamplerBase protected constructor(private val rng: UniformRandomProvider?) {
-    protected fun nextDouble(): Double = rng!!.nextDouble()
-    protected fun nextInt(): Int = rng!!.nextInt()
-    protected fun nextInt(max: Int): Int = rng!!.nextInt(max)
-    protected fun nextLong(): Long = rng!!.nextLong()
-    override fun toString(): String = "rng=$rng"
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/SharedStateContinuousSampler.kt

@@ -1,7 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.sampling.SharedStateSampler
-
-interface SharedStateContinuousSampler : ContinuousSampler,
-    SharedStateSampler<SharedStateContinuousSampler?> {
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/SharedStateDiscreteSampler.kt

@@ -1,7 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.sampling.SharedStateSampler
-
-interface SharedStateDiscreteSampler : DiscreteSampler,
-    SharedStateSampler<SharedStateDiscreteSampler?> { // Composite interface
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/commons/rng/sampling/distribution/SmallMeanPoissonSampler.kt

@@ -1,60 +0,0 @@
-package scientifik.kmath.commons.rng.sampling.distribution
-
-import scientifik.kmath.commons.rng.UniformRandomProvider
-import kotlin.math.ceil
-import kotlin.math.exp
-
-class SmallMeanPoissonSampler :
-    SharedStateDiscreteSampler {
-    private val p0: Double
-    private val limit: Int
-    private val rng: UniformRandomProvider
-
-    constructor(
-        rng: UniformRandomProvider,
-        mean: Double
-    ) {
-        this.rng = rng
-        require(mean > 0) { "mean is not strictly positive: $mean" }
-        p0 = exp(-mean)
-
-        limit = (if (p0 > 0) ceil(1000 * mean) else throw IllegalArgumentException("No p(x=0) probability for mean: $mean")).toInt()
-            // This excludes NaN values for the mean
-        // else
-        // The returned sample is bounded by 1000 * mean
-    }
-
-    private constructor(
-        rng: UniformRandomProvider,
-        source: SmallMeanPoissonSampler
-    ) {
-        this.rng = rng
-        p0 = source.p0
-        limit = source.limit
-    }
-
-    override fun sample(): Int {
-        var n = 0
-        var r = 1.0
-
-        while (n < limit) {
-            r *= rng.nextDouble()
-            if (r >= p0) n++ else break
-        }
-
-        return n
-    }
-
-    override fun toString(): String = "Small Mean Poisson deviate [$rng]"
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateDiscreteSampler =
-        SmallMeanPoissonSampler(rng, this)
-
-    companion object {
-        fun of(
-            rng: UniformRandomProvider,
-            mean: Double
-        ): SharedStateDiscreteSampler =
-            SmallMeanPoissonSampler(rng, mean)
-    }
-}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/Distribution.kt

@@ -1,5 +1,6 @@
 package scientifik.kmath.prob
 
+import kotlinx.coroutines.flow.first
 import scientifik.kmath.chains.Chain
 import scientifik.kmath.chains.collect
 import scientifik.kmath.structures.Buffer
@@ -69,6 +70,8 @@ fun <T : Any> Sampler<T>.sampleBuffer(
     }
 }
 
+suspend fun <T : Any> Sampler<T>.next(generator: RandomGenerator) = sample(generator).first()
+
 /**
  * Generate a bunch of samples from real distributions
  */

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/FactorizedDistribution.kt

@@ -12,7 +12,6 @@ interface NamedDistribution<T> : Distribution<Map<String, T>>
  * A multivariate distribution that has independent distributions for separate axis
  */
 class FactorizedDistribution<T>(val distributions: Collection<NamedDistribution<T>>) : NamedDistribution<T> {
-
     override fun probability(arg: Map<String, T>): Double {
         return distributions.fold(1.0) { acc, distr -> acc * distr.probability(arg) }
     }

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/RandomGenerator.kt

@@ -7,13 +7,11 @@ import kotlin.random.Random
  */
 interface RandomGenerator {
     fun nextBoolean(): Boolean
-
     fun nextDouble(): Double
     fun nextInt(): Int
     fun nextInt(until: Int): Int
     fun nextLong(): Long
     fun nextLong(until: Long): Long
-
     fun fillBytes(array: ByteArray, fromIndex: Int = 0, toIndex: Int = array.size)
     fun nextBytes(size: Int): ByteArray = ByteArray(size).also { fillBytes(it) }
 
@@ -28,21 +26,16 @@ interface RandomGenerator {
 
     companion object {
         val default by lazy { DefaultGenerator() }
-
         fun default(seed: Long) = DefaultGenerator(Random(seed))
     }
 }
 
-inline class DefaultGenerator(val random: Random = Random) : RandomGenerator {
+inline class DefaultGenerator(private val random: Random = Random) : RandomGenerator {
     override fun nextBoolean(): Boolean = random.nextBoolean()
-
     override fun nextDouble(): Double = random.nextDouble()
-
     override fun nextInt(): Int = random.nextInt()
     override fun nextInt(until: Int): Int = random.nextInt(until)
-
     override fun nextLong(): Long = random.nextLong()
-
     override fun nextLong(until: Long): Long = random.nextLong(until)
 
     override fun fillBytes(array: ByteArray, fromIndex: Int, toIndex: Int) {
@@ -50,6 +43,5 @@ inline class DefaultGenerator(val random: Random = Random) : RandomGenerator {
     }
 
     override fun nextBytes(size: Int): ByteArray = random.nextBytes(size)
-
     override fun fork(): RandomGenerator = RandomGenerator.default(random.nextLong())
 }

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/AhrensDieterExponentialSampler.kt

@@ -0,0 +1,68 @@
+package scientifik.kmath.prob.samplers
+
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+import scientifik.kmath.prob.chain
+import kotlin.math.ln
+import kotlin.math.pow
+
+class AhrensDieterExponentialSampler(val mean: Double) : Sampler<Double> {
+    init {
+        require(mean > 0) { "mean is not strictly positive: $mean" }
+    }
+
+    override fun sample(generator: RandomGenerator): Chain<Double> = generator.chain {
+        // Step 1:
+        var a = 0.0
+        var u = nextDouble()
+
+        // Step 2 and 3:
+        while (u < 0.5) {
+            a += EXPONENTIAL_SA_QI[0]
+            u *= 2.0
+        }
+
+        // Step 4 (now u >= 0.5):
+        u += u - 1
+        // Step 5:
+        if (u <= EXPONENTIAL_SA_QI[0]) return@chain mean * (a + u)
+        // Step 6:
+        var i = 0 // Should be 1, be we iterate before it in while using 0.
+        var u2 = nextDouble()
+        var umin = u2
+
+        // Step 7 and 8:
+        do {
+            ++i
+            u2 = nextDouble()
+            if (u2 < umin) umin = u2
+            // Step 8:
+        } while (u > EXPONENTIAL_SA_QI[i]) // Ensured to exit since EXPONENTIAL_SA_QI[MAX] = 1.
+
+        mean * (a + umin * EXPONENTIAL_SA_QI[0])
+    }
+
+    override fun toString(): String = "Ahrens-Dieter Exponential deviate"
+
+    companion object {
+        private val EXPONENTIAL_SA_QI = DoubleArray(16)
+
+        fun of(mean: Double): Sampler<Double> =
+            AhrensDieterExponentialSampler(mean)
+
+        init {
+            /**
+             * Filling EXPONENTIAL_SA_QI table.
+             * Note that we don't want qi = 0 in the table.
+             */
+            val ln2 = ln(2.0)
+            var qi = 0.0
+
+            EXPONENTIAL_SA_QI.indices.forEach { i ->
+                qi += ln2.pow(i + 1.0) / InternalUtils.factorial(i + 1)
+                EXPONENTIAL_SA_QI[i] = qi
+            }
+        }
+    }
+}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/BoxMullerNormalizedGaussianSampler.kt

@@ -0,0 +1,37 @@
+package scientifik.kmath.prob.samplers
+
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+import scientifik.kmath.prob.chain
+import kotlin.math.*
+
+class BoxMullerNormalizedGaussianSampler : NormalizedGaussianSampler, Sampler<Double> {
+    private var nextGaussian: Double = Double.NaN
+
+    override fun sample(generator: RandomGenerator): Chain<Double> = generator.chain {
+        val random: Double
+
+        if (nextGaussian.isNaN()) {
+            // Generate a pair of Gaussian numbers.
+            val x = nextDouble()
+            val y = nextDouble()
+            val alpha = 2 * PI * x
+            val r = sqrt(-2 * ln(y))
+            // Return the first element of the generated pair.
+            random = r * cos(alpha)
+            // Keep second element of the pair for next invocation.
+            nextGaussian = r * sin(alpha)
+        } else {
+            // Use the second element of the pair (generated at the
+            // previous invocation).
+            random = nextGaussian
+            // Both elements of the pair have been used.
+            nextGaussian = Double.NaN
+        }
+
+        random
+    }
+
+    override fun toString(): String = "Box-Muller normalized Gaussian deviate"
+}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/GaussianSampler.kt

@@ -0,0 +1,34 @@
+package scientifik.kmath.prob.samplers
+
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.chains.map
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+
+class GaussianSampler(
+    private val mean: Double,
+    private val standardDeviation: Double,
+    private val normalized: NormalizedGaussianSampler
+) : Sampler<Double> {
+
+    init {
+        require(standardDeviation > 0) { "standard deviation is not strictly positive: $standardDeviation" }
+    }
+
+    override fun sample(generator: RandomGenerator): Chain<Double> =
+        normalized.sample(generator).map { standardDeviation * it + mean }
+
+    override fun toString(): String = "Gaussian deviate [$normalized]"
+
+    companion object {
+        fun of(
+            normalized: NormalizedGaussianSampler,
+            mean: Double,
+            standardDeviation: Double
+        ) = GaussianSampler(
+            mean,
+            standardDeviation,
+            normalized
+        )
+    }
+}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/InternalGamma.kt

@@ -1,10 +1,10 @@
-package scientifik.kmath.commons.rng.sampling.distribution
+package scientifik.kmath.prob.samplers
 
 import kotlin.math.PI
 import kotlin.math.ln
 
 internal object InternalGamma {
-    const val LANCZOS_G = 607.0 / 128.0
+    private const val LANCZOS_G = 607.0 / 128.0
 
     private val LANCZOS_COEFFICIENTS = doubleArrayOf(
         0.99999999999999709182,

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/InternalUtils.kt

@@ -1,7 +1,5 @@
-package scientifik.kmath.commons.rng.sampling.distribution
+package scientifik.kmath.prob.samplers
 
-import scientifik.kmath.commons.rng.UniformRandomProvider
-import scientifik.kmath.commons.rng.sampling.SharedStateSampler
 import kotlin.math.ln
 import kotlin.math.min
 
@@ -20,8 +18,8 @@ internal object InternalUtils {
 
     fun factorial(n: Int): Long = FACTORIALS[n]
 
-    fun validateProbabilities(probabilities: DoubleArray?): Double {
-        require(!(probabilities == null || probabilities.isEmpty())) { "Probabilities must not be empty." }
+    fun validateProbabilities(probabilities: DoubleArray): Double {
+        require(probabilities.isNotEmpty()) { "Probabilities must not be empty." }
         var sumProb = 0.0
 
         probabilities.forEach { prob ->
@@ -33,22 +31,9 @@ internal object InternalUtils {
         return sumProb
     }
 
-    fun validateProbability(probability: Double): Unit =
-        require(!(probability < 0 || probability.isInfinite() || probability.isNaN())) { "Invalid probability: $probability" }
-
-    fun newNormalizedGaussianSampler(
-        sampler: NormalizedGaussianSampler,
-        rng: UniformRandomProvider
-    ): NormalizedGaussianSampler {
-        if (sampler !is SharedStateSampler<*>) throw UnsupportedOperationException("The underlying sampler cannot share state")
-
-        val newSampler: Any =
-            (sampler as SharedStateSampler<*>).withUniformRandomProvider(rng) as? NormalizedGaussianSampler
-                ?: throw UnsupportedOperationException(
-                    "The underlying sampler did not create a normalized Gaussian sampler"
-                )
-
-        return newSampler as NormalizedGaussianSampler
+    private fun validateProbability(probability: Double): Unit =
+        require(!(probability < 0 || probability.isInfinite() || probability.isNaN())) {
+            "Invalid probability: $probability"
         }
 
     class FactorialLog private constructor(
@@ -68,23 +53,19 @@ internal object InternalUtils {
                     BEGIN_LOG_FACTORIALS, endCopy)
             }
             // All values to be computed
-            else
-                endCopy =
-                    BEGIN_LOG_FACTORIALS
+            else endCopy = BEGIN_LOG_FACTORIALS
 
             // Compute remaining values.
             (endCopy until numValues).forEach { i ->
-                if (i < FACTORIALS.size) logFactorials[i] = ln(
-                    FACTORIALS[i].toDouble()) else logFactorials[i] =
-                    logFactorials[i - 1] + ln(i.toDouble())
+                if (i < FACTORIALS.size)
+                    logFactorials[i] = ln(FACTORIALS[i].toDouble())
+                else
+                    logFactorials[i] = logFactorials[i - 1] + ln(i.toDouble())
             }
         }
 
         fun withCache(cacheSize: Int): FactorialLog =
-            FactorialLog(
-                cacheSize,
-                logFactorials
-            )
+            FactorialLog(cacheSize, logFactorials)
 
         fun value(n: Int): Double {
             if (n < logFactorials.size)
@@ -98,10 +79,7 @@ internal object InternalUtils {
 
         companion object {
             fun create(): FactorialLog =
-                FactorialLog(
-                    0,
-                    null
-                )
+                FactorialLog(0, null)
         }
     }
 }

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/KempSmallMeanPoissonSampler.kt

@@ -1,14 +1,16 @@
-package scientifik.kmath.commons.rng.sampling.distribution
+package scientifik.kmath.prob.samplers
 
-import scientifik.kmath.commons.rng.UniformRandomProvider
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+import scientifik.kmath.prob.chain
 import kotlin.math.exp
 
 class KempSmallMeanPoissonSampler private constructor(
-    private val rng: UniformRandomProvider,
     private val p0: Double,
     private val mean: Double
-) : SharedStateDiscreteSampler {
-    override fun sample(): Int {
+) : Sampler<Int> {
+    override fun sample(generator: RandomGenerator): Chain<Int> = generator.chain {
         // Note on the algorithm:
         // - X is the unknown sample deviate (the output of the algorithm)
         // - x is the current value from the distribution
@@ -16,7 +18,7 @@ class KempSmallMeanPoissonSampler private constructor(
         // - u is effectively the cumulative probability that the sample X
         //   is equal or above the current value x, p(X>=x)
         // So if p(X>=x) > p(X=x) the sample must be above x, otherwise it is x
-        var u = rng.nextDouble()
+        var u = nextDouble()
         var x = 0
         var p = p0
 
@@ -28,31 +30,20 @@ class KempSmallMeanPoissonSampler private constructor(
             // The algorithm listed in Kemp (1981) does not check that the rolling probability
             // is positive. This check is added to ensure no errors when the limit of the summation
             // 1 - sum(p(x)) is above 0 due to cumulative error in floating point arithmetic.
-            if (p == 0.0) return x
+            if (p == 0.0) return@chain x
         }
 
-        return x
+        x
     }
 
-    override fun toString(): String = "Kemp Small Mean Poisson deviate [$rng]"
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateDiscreteSampler =
-        KempSmallMeanPoissonSampler(rng, p0, mean)
+    override fun toString(): String = "Kemp Small Mean Poisson deviate"
 
     companion object {
-        fun of(
-            rng: UniformRandomProvider,
-            mean: Double
-        ): SharedStateDiscreteSampler {
+        fun of(mean: Double): KempSmallMeanPoissonSampler {
             require(mean > 0) { "Mean is not strictly positive: $mean" }
             val p0: Double = exp(-mean)
-
             // Probability must be positive. As mean increases then p(0) decreases.
-            if (p0 > 0) return KempSmallMeanPoissonSampler(
-                rng,
-                p0,
-                mean
-            )
+            if (p0 > 0) return KempSmallMeanPoissonSampler(p0, mean)
             throw IllegalArgumentException("No probability for mean: $mean")
         }
     }

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/LargeMeanPoissonSampler.kt

@@ -0,0 +1,132 @@
+package scientifik.kmath.prob.samplers
+
+import kotlinx.coroutines.flow.first
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.chains.ConstantChain
+import scientifik.kmath.chains.SimpleChain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+import scientifik.kmath.prob.next
+import kotlin.math.*
+
+class LargeMeanPoissonSampler(val mean: Double) : Sampler<Int> {
+    private val exponential: Sampler<Double> =
+        AhrensDieterExponentialSampler.of(1.0)
+    private val gaussian: Sampler<Double> =
+        ZigguratNormalizedGaussianSampler()
+    private val factorialLog: InternalUtils.FactorialLog = NO_CACHE_FACTORIAL_LOG!!
+    private val lambda: Double = floor(mean)
+    private val logLambda: Double = ln(lambda)
+    private val logLambdaFactorial: Double = getFactorialLog(lambda.toInt())
+    private val delta: Double = sqrt(lambda * ln(32 * lambda / PI + 1))
+    private val halfDelta: Double = delta / 2
+    private val twolpd: Double = 2 * lambda + delta
+    private val c1: Double = 1 / (8 * lambda)
+    private val a1: Double = sqrt(PI * twolpd) * exp(c1)
+    private val a2: Double = twolpd / delta * exp(-delta * (1 + delta) / twolpd)
+    private val aSum: Double = a1 + a2 + 1
+    private val p1: Double = a1 / aSum
+    private val p2: Double = a2 / aSum
+
+    private val smallMeanPoissonSampler: Sampler<Int> = if (mean - lambda < Double.MIN_VALUE)
+        NO_SMALL_MEAN_POISSON_SAMPLER
+    else  // Not used.
+        KempSmallMeanPoissonSampler.of(mean - lambda)
+
+    init {
+        require(mean >= 1) { "mean is not >= 1: $mean" }
+        // The algorithm is not valid if Math.floor(mean) is not an integer.
+        require(mean <= MAX_MEAN) { "mean $mean > $MAX_MEAN" }
+    }
+
+    override fun sample(generator: RandomGenerator): Chain<Int> = SimpleChain {
+        // This will never be null. It may be a no-op delegate that returns zero.
+        val y2 = smallMeanPoissonSampler.next(generator)
+        var x: Double
+        var y: Double
+        var v: Double
+        var a: Int
+        var t: Double
+        var qr: Double
+        var qa: Double
+
+        while (true) {
+            // Step 1:
+            val u = generator.nextDouble()
+
+            if (u <= p1) {
+                // Step 2:
+                val n = gaussian.next(generator)
+                x = n * sqrt(lambda + halfDelta) - 0.5
+                if (x > delta || x < -lambda) continue
+                y = if (x < 0) floor(x) else ceil(x)
+                val e = exponential.next(generator)
+                v = -e - 0.5 * n * n + c1
+            } else {
+                // Step 3:
+                if (u > p1 + p2) {
+                    y = lambda
+                    break
+                }
+
+                x = delta + twolpd / delta * exponential.next(generator)
+                y = ceil(x)
+                v = -exponential.next(generator) - delta * (x + 1) / twolpd
+            }
+
+            // The Squeeze Principle
+            // Step 4.1:
+            a = if (x < 0) 1 else 0
+            t = y * (y + 1) / (2 * lambda)
+
+            // Step 4.2
+            if (v < -t && a == 0) {
+                y += lambda
+                break
+            }
+
+            // Step 4.3:
+            qr = t * ((2 * y + 1) / (6 * lambda) - 1)
+            qa = qr - t * t / (3 * (lambda + a * (y + 1)))
+
+            // Step 4.4:
+            if (v < qa) {
+                y += lambda
+                break
+            }
+
+            // Step 4.5:
+            if (v > qr) continue
+
+            // Step 4.6:
+            if (v < y * logLambda - getFactorialLog((y + lambda).toInt()) + logLambdaFactorial) {
+                y += lambda
+                break
+            }
+        }
+
+        min(y2 + y.toLong(), Int.MAX_VALUE.toLong()).toInt()
+    }
+
+    private fun getFactorialLog(n: Int): Double = factorialLog.value(n)
+
+    override fun toString(): String = "Large Mean Poisson deviate"
+
+    companion object {
+        private const val MAX_MEAN = 0.5 * Int.MAX_VALUE
+        private var NO_CACHE_FACTORIAL_LOG: InternalUtils.FactorialLog? = null
+
+        private val NO_SMALL_MEAN_POISSON_SAMPLER = object : Sampler<Int> {
+            override fun sample(generator: RandomGenerator): Chain<Int> = ConstantChain(0)
+        }
+
+        fun of(mean: Double): LargeMeanPoissonSampler =
+            LargeMeanPoissonSampler(mean)
+
+        init {
+            // Create without a cache.
+            NO_CACHE_FACTORIAL_LOG =
+                InternalUtils.FactorialLog.create()
+        }
+    }
+}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/MarsagliaNormalizedGaussianSampler.kt

@@ -1,35 +1,42 @@
-package scientifik.kmath.commons.rng.sampling.distribution
+package scientifik.kmath.prob.samplers
 
-import scientifik.kmath.commons.rng.UniformRandomProvider
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+import scientifik.kmath.prob.chain
 import kotlin.math.ln
 import kotlin.math.sqrt
 
-class MarsagliaNormalizedGaussianSampler(private val rng: UniformRandomProvider) :
-    NormalizedGaussianSampler,
-    SharedStateContinuousSampler {
+class MarsagliaNormalizedGaussianSampler : NormalizedGaussianSampler, Sampler<Double> {
     private var nextGaussian = Double.NaN
 
-    override fun sample(): Double {
+    override fun sample(generator: RandomGenerator): Chain<Double> = generator.chain {
         if (nextGaussian.isNaN()) {
+            val alpha: Double
+            var x: Double
+
             // Rejection scheme for selecting a pair that lies within the unit circle.
             while (true) {
                 // Generate a pair of numbers within [-1 , 1).
-                val x = 2.0 * rng.nextDouble() - 1.0
-                val y = 2.0 * rng.nextDouble() - 1.0
+                x = 2.0 * generator.nextDouble() - 1.0
+                val y = 2.0 * generator.nextDouble() - 1.0
                 val r2 = x * x + y * y
+
                 if (r2 < 1 && r2 > 0) {
                     // Pair (x, y) is within unit circle.
-                    val alpha = sqrt(-2 * ln(r2) / r2)
+                    alpha = sqrt(-2 * ln(r2) / r2)
 
                     // Keep second element of the pair for next invocation.
                     nextGaussian = alpha * y
 
                     // Return the first element of the generated pair.
-                    return alpha * x
+                    break
                 }
-
                 // Pair is not within the unit circle: Generate another one.
             }
+
+            // Return the first element of the generated pair.
+            alpha * x
         } else {
             // Use the second element of the pair (generated at the
             // previous invocation).
@@ -37,18 +44,9 @@ class MarsagliaNormalizedGaussianSampler(private val rng: UniformRandomProvider)
 
             // Both elements of the pair have been used.
             nextGaussian = Double.NaN
-            return r
+            r
         }
     }
 
-    override fun toString(): String = "Box-Muller (with rejection) normalized Gaussian deviate [$rng]"
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateContinuousSampler =
-        MarsagliaNormalizedGaussianSampler(rng)
-
-    companion object {
-        @Suppress("UNCHECKED_CAST")
-        fun <S> of(rng: UniformRandomProvider): S where S : NormalizedGaussianSampler?, S : SharedStateContinuousSampler? =
-            MarsagliaNormalizedGaussianSampler(rng) as S
-    }
+    override fun toString(): String = "Box-Muller (with rejection) normalized Gaussian deviate"
 }

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/NormalizedGaussianSampler.kt

@@ -0,0 +1,5 @@
+package scientifik.kmath.prob.samplers
+
+import scientifik.kmath.prob.Sampler
+
+interface NormalizedGaussianSampler : Sampler<Double>

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/PoissonSampler.kt

@@ -0,0 +1,29 @@
+package scientifik.kmath.prob.samplers
+
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+
+
+class PoissonSampler(
+    mean: Double
+) : Sampler<Int> {
+    private val poissonSamplerDelegate: Sampler<Int>
+
+    init {
+        // Delegate all work to specialised samplers.
+        poissonSamplerDelegate = of(mean)
+    }
+
+    override fun sample(generator: RandomGenerator): Chain<Int> = poissonSamplerDelegate.sample(generator)
+    override fun toString(): String = poissonSamplerDelegate.toString()
+
+    companion object {
+        private const val PIVOT = 40.0
+
+        fun of(mean: Double) =// Each sampler should check the input arguments.
+            if (mean < PIVOT) SmallMeanPoissonSampler.of(
+                mean
+            ) else LargeMeanPoissonSampler.of(mean)
+    }
+}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/SmallMeanPoissonSampler.kt

@@ -0,0 +1,43 @@
+package scientifik.kmath.prob.samplers
+
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.chains.SimpleChain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+import scientifik.kmath.prob.chain
+import kotlin.math.ceil
+import kotlin.math.exp
+
+class SmallMeanPoissonSampler(mean: Double) : Sampler<Int> {
+    private val p0: Double
+    private val limit: Int
+
+    init {
+        require(mean > 0) { "mean is not strictly positive: $mean" }
+        p0 = exp(-mean)
+
+        limit = (if (p0 > 0)
+            ceil(1000 * mean)
+        else
+            throw IllegalArgumentException("No p(x=0) probability for mean: $mean")).toInt()
+    }
+
+    override fun sample(generator: RandomGenerator): Chain<Int> = generator.chain {
+        var n = 0
+        var r = 1.0
+
+        while (n < limit) {
+            r *= nextDouble()
+            if (r >= p0) n++ else break
+        }
+
+        n
+    }
+
+    override fun toString(): String = "Small Mean Poisson deviate"
+
+    companion object {
+        fun of(mean: Double): SmallMeanPoissonSampler =
+            SmallMeanPoissonSampler(mean)
+    }
+}

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/samplers/ZigguratNormalizedGaussianSampler.kt

@@ -1,38 +1,76 @@
-package scientifik.kmath.commons.rng.sampling.distribution
+package scientifik.kmath.prob.samplers
 
-import scientifik.kmath.commons.rng.UniformRandomProvider
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.chains.SimpleChain
+import scientifik.kmath.prob.RandomGenerator
+import scientifik.kmath.prob.Sampler
+import scientifik.kmath.prob.chain
 import kotlin.math.*
 
-class ZigguratNormalizedGaussianSampler(private val rng: UniformRandomProvider) :
-    NormalizedGaussianSampler,
-    SharedStateContinuousSampler {
+class ZigguratNormalizedGaussianSampler() :
+    NormalizedGaussianSampler, Sampler<Double> {
+
+    private fun sampleOne(generator: RandomGenerator): Double {
+        val j = generator.nextLong()
+        val i = (j and LAST.toLong()).toInt()
+        return if (abs(j) < K[i]) j * W[i] else fix(generator, j, i)
+    }
+
+    override fun sample(generator: RandomGenerator): Chain<Double> = generator.chain { sampleOne(this) }
+
+    override fun toString(): String = "Ziggurat normalized Gaussian deviate"
+
+    private fun fix(
+        generator: RandomGenerator,
+        hz: Long,
+        iz: Int
+    ): Double {
+        var x: Double
+        var y: Double
+        x = hz * W[iz]
+
+        return if (iz == 0) {
+            // Base strip.
+            // This branch is called about 5.7624515E-4 times per sample.
+            do {
+                y = -ln(generator.nextDouble())
+                x = -ln(generator.nextDouble()) * ONE_OVER_R
+            } while (y + y < x * x)
+
+            val out = R + x
+            if (hz > 0) out else -out
+        } else {
+            // Wedge of other strips.
+            // This branch is called about 0.027323 times per sample.
+            // else
+            // Try again.
+            // This branch is called about 0.012362 times per sample.
+            if (F[iz] + generator.nextDouble() * (F[iz - 1] - F[iz]) < gauss(
+                    x
+                )
+            ) x else sampleOne(generator)
+        }
+    }
 
     companion object {
-        private const val R = 3.442619855899
+        private const val R: Double = 3.442619855899
         private const val ONE_OVER_R: Double = 1 / R
         private const val V = 9.91256303526217e-3
         private val MAX: Double = 2.0.pow(63.0)
         private val ONE_OVER_MAX: Double = 1.0 / MAX
-        private const val LEN = 128
+        private const val LEN: Int = 128
         private const val LAST: Int = LEN - 1
-        private val K = LongArray(LEN)
-        private val W = DoubleArray(LEN)
-        private val F = DoubleArray(LEN)
+        private val K: LongArray = LongArray(LEN)
+        private val W: DoubleArray = DoubleArray(LEN)
+        private val F: DoubleArray = DoubleArray(LEN)
         private fun gauss(x: Double): Double = exp(-0.5 * x * x)
 
-        @Suppress("UNCHECKED_CAST")
-        fun <S> of(rng: UniformRandomProvider): S where S : NormalizedGaussianSampler?, S : SharedStateContinuousSampler? =
-            ZigguratNormalizedGaussianSampler(rng) as S
-
         init {
             // Filling the tables.
-            var d =
-                R
+            var d = R
             var t = d
             var fd =
-                gauss(
-                    d
-                )
+                gauss(d)
             val q = V / fd
             K[0] = (d / q * MAX).toLong()
             K[1] = 0
@@ -54,46 +92,4 @@ class ZigguratNormalizedGaussianSampler(private val rng: UniformRandomProvider)
             }
         }
     }
-
-    override fun sample(): Double {
-        val j = rng.nextLong()
-        val i = (j and LAST.toLong()).toInt()
-        return if (abs(j) < K[i]) j * W[i] else fix(j, i)
-    }
-
-    override fun toString(): String = "Ziggurat normalized Gaussian deviate [$rng]"
-
-    private fun fix(
-        hz: Long,
-        iz: Int
-    ): Double {
-        var x: Double
-        var y: Double
-        x = hz * W[iz]
-
-        return if (iz == 0) {
-            // Base strip.
-            // This branch is called about 5.7624515E-4 times per sample.
-            do {
-                y = -ln(rng.nextDouble())
-                x = -ln(rng.nextDouble()) * ONE_OVER_R
-            } while (y + y < x * x)
-
-            val out = R + x
-            if (hz > 0) out else -out
-        } else {
-            // Wedge of other strips.
-            // This branch is called about 0.027323 times per sample.
-            // else
-            // Try again.
-            // This branch is called about 0.012362 times per sample.
-            if (F[iz] + rng.nextDouble() * (F[iz - 1] - F[iz]) < gauss(
-                    x
-                )
-            ) x else sample()
-        }
-    }
-
-    override fun withUniformRandomProvider(rng: UniformRandomProvider): SharedStateContinuousSampler =
-        ZigguratNormalizedGaussianSampler(rng)
 }

kmath-prob/src/jvmMain/kotlin/scientifik/kmath/prob/DistributionsJVM.kt

@@ -1,66 +0,0 @@
-package scientifik.kmath.prob
-
-import scientifik.kmath.commons.rng.sampling.distribution.ContinuousSampler
-import scientifik.kmath.commons.rng.sampling.distribution.DiscreteSampler
-import scientifik.kmath.commons.rng.sampling.distribution.GaussianSampler
-import scientifik.kmath.commons.rng.sampling.distribution.PoissonSampler
-import kotlin.math.PI
-import kotlin.math.exp
-import kotlin.math.pow
-import kotlin.math.sqrt
-
-fun Distribution.Companion.normal(
-    method: NormalSamplerMethod = NormalSamplerMethod.Ziggurat
-): Distribution<Double> = object : ContinuousSamplerDistribution() {
-    override fun buildCMSampler(generator: RandomGenerator): ContinuousSampler {
-        val provider = generator.asUniformRandomProvider()
-        return normalSampler(method, provider)
-    }
-
-    override fun probability(arg: Double): Double {
-        return exp(-arg.pow(2) / 2) / sqrt(PI * 2)
-    }
-}
-
-fun Distribution.Companion.normal(
-    mean: Double,
-    sigma: Double,
-    method: NormalSamplerMethod = NormalSamplerMethod.Ziggurat
-): ContinuousSamplerDistribution = object : ContinuousSamplerDistribution() {
-    private val sigma2 = sigma.pow(2)
-    private val norm = sigma * sqrt(PI * 2)
-
-    override fun buildCMSampler(generator: RandomGenerator): ContinuousSampler {
-        val provider = generator.asUniformRandomProvider()
-        val normalizedSampler = normalSampler(method, provider)
-        return GaussianSampler(
-            normalizedSampler,
-            mean,
-            sigma
-        )
-    }
-
-    override fun probability(arg: Double): Double {
-        return exp(-(arg - mean).pow(2) / 2 / sigma2) / norm
-    }
-}
-
-fun Distribution.Companion.poisson(
-    lambda: Double
-): DiscreteSamplerDistribution = object : DiscreteSamplerDistribution() {
-
-    override fun buildSampler(generator: RandomGenerator): DiscreteSampler {
-        return PoissonSampler.of(generator.asUniformRandomProvider(), lambda)
-    }
-
-    private val computedProb: HashMap<Int, Double> = hashMapOf(0 to exp(-lambda))
-
-    override fun probability(arg: Int): Double {
-        require(arg >= 0) { "The argument must be >= 0" }
-
-        return if (arg > 40)
-            exp(-(arg - lambda).pow(2) / 2 / lambda) / sqrt(2 * PI * lambda)
-        else
-            computedProb.getOrPut(arg) { probability(arg - 1) * lambda / arg }
-    }
-}

kmath-prob/src/jvmMain/kotlin/scientifik/kmath/prob/RandomSourceGenerator.kt

@@ -1,11 +1,10 @@
 package scientifik.kmath.prob
 
 import org.apache.commons.rng.simple.RandomSource
-import scientifik.kmath.commons.rng.UniformRandomProvider
 
-class RandomSourceGenerator(val source: RandomSource, seed: Long?) :
+class RandomSourceGenerator(private val source: RandomSource, seed: Long?) :
     RandomGenerator {
-    internal val random = seed?.let {
+    private val random = seed?.let {
         RandomSource.create(source, seed)
     } ?: RandomSource.create(source)
 
@@ -24,24 +23,6 @@ class RandomSourceGenerator(val source: RandomSource, seed: Long?) :
     override fun fork(): RandomGenerator = RandomSourceGenerator(source, nextLong())
 }
 
-/**
- * Represent this [RandomGenerator] as commons-rng [UniformRandomProvider] preserving and mirroring its current state.
- * Getting new value from one of those changes the state of another.
- */
-fun RandomGenerator.asUniformRandomProvider(): UniformRandomProvider = if (this is RandomSourceGenerator) {
-    object : UniformRandomProvider {
-        override fun nextBytes(bytes: ByteArray) = random.nextBytes(bytes)
-        override fun nextBytes(bytes: ByteArray, start: Int, len: Int) = random.nextBytes(bytes, start, len)
-        override fun nextInt(): Int = random.nextInt()
-        override fun nextInt(n: Int): Int = random.nextInt(n)
-        override fun nextLong(): Long = random.nextLong()
-        override fun nextLong(n: Long): Long = random.nextLong(n)
-        override fun nextBoolean(): Boolean = random.nextBoolean()
-        override fun nextFloat(): Float = random.nextFloat()
-        override fun nextDouble(): Double = random.nextDouble()
-    }
-} else RandomGeneratorProvider(this)
-
 fun RandomGenerator.Companion.fromSource(source: RandomSource, seed: Long? = null): RandomSourceGenerator =
     RandomSourceGenerator(source, seed)