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Changed the order of Polynomial coefficients back

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This commit is contained in:
Andrius Dagys 2016-04-05 17:40:42 +01:00
parent b728bd3b9d
commit 40443f68cb
1 changed files with 7 additions and 5 deletions
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12
core/src/main/kotlin/core/math/Interpolators.kt
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@ -8,7 +8,7 @@ import java.util.*
* Implementation uses the Natural Cubic Spline algorithm as described in * Implementation uses the Natural Cubic Spline algorithm as described in
* R. L. Burden and J. D. Faires (2011), *Numerical Analysis*. 9th ed. Boston, MA: Brooks/Cole, Cengage Learning. p149-150. * R. L. Burden and J. D. Faires (2011), *Numerical Analysis*. 9th ed. Boston, MA: Brooks/Cole, Cengage Learning. p149-150.
*/ */
class CubicSplineInterpolator(val xs: DoubleArray, val ys: DoubleArray) { class CubicSplineInterpolator(private val xs: DoubleArray, private val ys: DoubleArray) {
init { init {
require(xs.size == ys.size) { "x and y dimensions should match: ${xs.size} != ${ys.size}" } require(xs.size == ys.size) { "x and y dimensions should match: ${xs.size} != ${ys.size}" }
require(xs.size >= 3) { "At least 3 data points are required for interpolation, received: ${xs.size}" } require(xs.size >= 3) { "At least 3 data points are required for interpolation, received: ${xs.size}" }
@ -54,7 +54,7 @@ class CubicSplineInterpolator(val xs: DoubleArray, val ys: DoubleArray) {
val segmentMap = TreeMap<Double, Polynomial>() val segmentMap = TreeMap<Double, Polynomial>()
for (i in 0..n - 1) { for (i in 0..n - 1) {
val coefficients = doubleArrayOf(d[i], c[i], b[i], ys[i]) val coefficients = doubleArrayOf(ys[i], b[i], c[i], d[i])
segmentMap.put(xs[i], Polynomial(coefficients)) segmentMap.put(xs[i], Polynomial(coefficients))
} }
return SplineFunction(segmentMap) return SplineFunction(segmentMap)
@ -63,10 +63,12 @@ class CubicSplineInterpolator(val xs: DoubleArray, val ys: DoubleArray) {
/** /**
* Represents a polynomial function of arbitrary degree * Represents a polynomial function of arbitrary degree
* @param coefficients polynomial coefficients in descending order (highest degree first) * @param coefficients polynomial coefficients in the order of degree (constant first, followed by higher degree term coefficients)
*/ */
class Polynomial(private val coefficients: DoubleArray) { class Polynomial(private val coefficients: DoubleArray) {
fun getValue(x: Double) = coefficients.fold(0.0, { result, c -> result * x + c }) private val reversedCoefficients = coefficients.reversed()
fun getValue(x: Double) = reversedCoefficients.fold(0.0, { result, c -> result * x + c })
} }
/** /**
@ -75,7 +77,7 @@ class Polynomial(private val coefficients: DoubleArray) {
* *
* @param segmentMap a mapping between a knot and the polynomial that covers the subsequent interval * @param segmentMap a mapping between a knot and the polynomial that covers the subsequent interval
*/ */
class SplineFunction(val segmentMap: TreeMap<Double, Polynomial>) { class SplineFunction(private val segmentMap: TreeMap<Double, Polynomial>) {
fun getValue(x: Double): Double { fun getValue(x: Double): Double {
val (knot, polynomial) = segmentMap.floorEntry(x) val (knot, polynomial) = segmentMap.floorEntry(x)
return polynomial.getValue(x - knot) return polynomial.getValue(x - knot)