59 lines
1.2 KiB
Go
59 lines
1.2 KiB
Go
package utils
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import (
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"math"
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"gonum.org/v1/gonum/mat"
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)
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type PolynomialInterpolator struct {
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Degree int
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Coeffs []float64
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}
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func (p *PolynomialInterpolator) Fit(x, y []float64) error {
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if p.Degree == 0 {
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p.Degree = len(x) - 1
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}
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degree := p.Degree
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n := len(x)
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// Create the Vandermonde matrix
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vander := mat.NewDense(n, degree+1, nil)
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for i := 0; i < n; i++ {
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for j := 0; j <= degree; j++ {
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vander.Set(i, j, math.Pow(x[i], float64(j)))
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}
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}
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// Create the right-hand side vector
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yVec := mat.NewVecDense(n, y)
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// Solve the least squares problem
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var qr mat.QR
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qr.Factorize(vander)
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coeffs := mat.NewDense(degree+1, 1, nil)
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err := qr.SolveTo(coeffs, false, yVec)
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p.Coeffs = coeffs.RawMatrix().Data
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return err
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}
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func (p PolynomialInterpolator) Predict(x float64) float64 {
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var y float64
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for i, coeff := range p.Coeffs {
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y += coeff * math.Pow(x, float64(i))
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}
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return y
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}
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func InterpPolynomial(x []float64, y []float64, xq float64, degree int) float64 {
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if len(x) != len(y) {
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return 0.0
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}
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start, end := FindClosestSubset(x, xq, degree+1)
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interp := &PolynomialInterpolator{Degree: degree}
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interp.Fit(x[start:end+1], y[start:end+1])
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return interp.Predict(xq)
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}
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