Fix Interpolation

examples/src/main/kotlin/space/kscience/kmath/functions/interpolate.kt

@@ -33,24 +33,21 @@ fun main() {
         data.map { it.second }.toDoubleArray()
     )
 
-    println(function(2.0))
-    println(cmInterpolate.value(2.0))
 
-//
+    Plotly.plot {
-//    Plotly.plot {
+        scatter {
-//        scatter {
+            name = "interpolated"
-//            name = "interpolated"
+            x.numbers = data.map { it.first }
-//            x.numbers = data.map { it.first }
+            y.numbers = x.doubles.map { function(it) }
-//            y.numbers = x.doubles.map { function(it) }
+        }
-//        }
+        scatter {
-//        scatter {
+            name = "original"
-//            name = "original"
+            functionXY(0.0..(2 * PI), 0.1) { sin(it) }
-//            functionXY(0.0..(2 * PI), 0.1) { sin(it) }
+        }
-//        }
+        scatter {
-//        scatter {
+            name = "cm"
-//            name = "cm"
+            x.numbers = data.map { it.first }
-//            x.numbers = data.map { it.first }
+            y.numbers = x.doubles.map { cmInterpolate.value(it) }
-//            y.numbers = x.doubles.map { cmInterpolate.value(it) }
+        }
-//        }
+    }.makeFile()
-//    }.makeFile()
 }

kmath-ejml/src/main/kotlin/space/kscience/kmath/ejml/_generated.kt

@@ -8,18 +8,28 @@
 package space.kscience.kmath.ejml
 
 import org.ejml.data.*
+import org.ejml.dense.row.CommonOps_DDRM
+import org.ejml.dense.row.CommonOps_FDRM
+import org.ejml.dense.row.factory.DecompositionFactory_DDRM
+import org.ejml.dense.row.factory.DecompositionFactory_FDRM
+import org.ejml.sparse.FillReducing
+import org.ejml.sparse.csc.CommonOps_DSCC
+import org.ejml.sparse.csc.CommonOps_FSCC
+import org.ejml.sparse.csc.factory.DecompositionFactory_DSCC
+import org.ejml.sparse.csc.factory.DecompositionFactory_FSCC
+import org.ejml.sparse.csc.factory.LinearSolverFactory_DSCC
+import org.ejml.sparse.csc.factory.LinearSolverFactory_FSCC
 import space.kscience.kmath.linear.*
-import space.kscience.kmath.operations.*
-import space.kscience.kmath.structures.*
-import space.kscience.kmath.misc.*
-import kotlin.reflect.*
-import org.ejml.dense.row.*
-import org.ejml.dense.row.factory.*
-import org.ejml.sparse.*
-import org.ejml.sparse.csc.*
-import org.ejml.sparse.csc.factory.*
-import space.kscience.kmath.nd.*
 import space.kscience.kmath.linear.Matrix
+import space.kscience.kmath.misc.UnstableKMathAPI
+import space.kscience.kmath.nd.StructureFeature
+import space.kscience.kmath.operations.DoubleField
+import space.kscience.kmath.operations.FloatField
+import space.kscience.kmath.operations.invoke
+import space.kscience.kmath.structures.DoubleBuffer
+import space.kscience.kmath.structures.FloatBuffer
+import kotlin.reflect.KClass
+import kotlin.reflect.cast
 
 /**
  * [EjmlVector] specialization for [Double].

kmath-functions/src/commonMain/kotlin/space/kscience/kmath/interpolation/SplineInterpolator.kt

@@ -10,8 +10,10 @@ import space.kscience.kmath.functions.OrderedPiecewisePolynomial
 import space.kscience.kmath.functions.PiecewisePolynomial
 import space.kscience.kmath.functions.Polynomial
 import space.kscience.kmath.misc.UnstableKMathAPI
+import space.kscience.kmath.operations.DoubleField
 import space.kscience.kmath.operations.Field
 import space.kscience.kmath.operations.invoke
+import space.kscience.kmath.structures.DoubleBuffer
 import space.kscience.kmath.structures.MutableBufferFactory
 
 /**
@@ -56,10 +58,23 @@ public class SplineInterpolator<T : Comparable<T>>(
                 val a = points.y[j]
                 val b = (points.y[j + 1] - points.y[j]) / h[j] - h[j] * (cOld + 2.0 * c) / 3.0
                 val d = (cOld - c) / (3.0 * h[j])
-                val polynomial = Polynomial(a, b, c, d)
+                val x0 = points.x[j]
+                val x02 = x0 * x0
+                val x03 = x02 * x0
+                //Shift coefficients to represent absolute polynomial instead of one with an offset
+                val polynomial = Polynomial(
+                    a - b * x0 + c * x02 - d * x03,
+                    b - 2*c*x0 + 3*d*x02,
+                    c - 3*d*x0,
+                    d
+                )
                 cOld = c
-                putLeft(points.x[j], polynomial)
+                putLeft(x0, polynomial)
             }
         }
     }
+
+    public companion object {
+        public val double: SplineInterpolator<Double> = SplineInterpolator(DoubleField, ::DoubleBuffer)
+    }
 }

kmath-functions/src/commonTest/kotlin/space/kscience/kmath/interpolation/SplineInterpolatorTest.kt

@@ -8,7 +8,6 @@ package space.kscience.kmath.interpolation
 import space.kscience.kmath.functions.PiecewisePolynomial
 import space.kscience.kmath.functions.asFunction
 import space.kscience.kmath.operations.DoubleField
-import space.kscience.kmath.structures.DoubleBuffer
 import kotlin.math.PI
 import kotlin.math.sin
 import kotlin.test.Test
@@ -22,14 +21,12 @@ internal class SplineInterpolatorTest {
             x to sin(x)
         }
 
-        val polynomial: PiecewisePolynomial<Double> = SplineInterpolator(
+        val polynomial: PiecewisePolynomial<Double> = SplineInterpolator.double.interpolatePolynomials(data)
-            DoubleField, ::DoubleBuffer
-        ).interpolatePolynomials(data)
 
-        val function = polynomial.asFunction(DoubleField)
+        val function = polynomial.asFunction(DoubleField, Double.NaN)
-        assertEquals(null, function(-1.0))
+        assertEquals(Double.NaN, function(-1.0))
-        assertEquals(sin(0.5), function(0.5)!!, 0.1)
+        assertEquals(sin(0.5), function(0.5), 0.1)
-        assertEquals(sin(1.5), function(1.5)!!, 0.1)
+        assertEquals(sin(1.5), function(1.5), 0.1)
-        assertEquals(sin(2.0), function(2.0)!!, 0.1)
+        assertEquals(sin(2.0), function(2.0), 0.1)
     }
 }