added shiftOperartion and diff

kmath-stat/src/commonMain/kotlin/space/kscience/kmath/series/SeriesAlgebra.kt

@@ -199,12 +199,25 @@ public open class SeriesAlgebra<T, out A : Ring<T>, out BA : BufferAlgebra<T, A>
         }
     }
 
+    /**
+     * Zip buffer with itself, but shifted
+     * */
+    public inline fun Buffer<T>.shiftOp(
+        shift: Int = 1,
+        crossinline operation: A.(left: T, right: T) -> T
+    ): Buffer<T> {
+        val shifted = this.moveTo(this.startOffset+shift)
+        return zip(shifted, operation)
+    }
+
     override fun Buffer<T>.unaryMinus(): Buffer<T> = map { -it }
 
     override fun add(left: Buffer<T>, right: Buffer<T>): Series<T> = left.zip(right) { l, r -> l + r }
 
     override fun multiply(left: Buffer<T>, right: Buffer<T>): Buffer<T> = left.zip(right) { l, r -> l * r }
 
+    public inline fun Buffer<T>.diff(): Buffer<T> = this.shiftOp {l, r -> r - l}
+
     public companion object
 }