go-chart/matrix/regression.go

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package matrix
import "errors"
var (
// ErrPolyRegArraysSameLength is a common error.
ErrPolyRegArraysSameLength = errors.New("polynomial array inputs must be the same length")
)
// Poly returns the polynomial regress of a given degree over the given values.
func Poly(xvalues, yvalues []float64, degree int) ([]float64, error) {
if len(xvalues) != len(yvalues) {
return nil, ErrPolyRegArraysSameLength
}
m := len(yvalues)
n := degree + 1
y := New(m, 1, yvalues...)
x := Zero(m, n)
for i := 0; i < m; i++ {
ip := float64(1)
for j := 0; j < n; j++ {
x.Set(i, j, ip)
ip *= xvalues[i]
}
}
q, r := x.QR()
qty, err := q.Transpose().Times(y)
if err != nil {
return nil, err
}
c := make([]float64, n)
for i := n - 1; i >= 0; i-- {
c[i] = qty.Get(i, 0)
for j := i + 1; j < n; j++ {
c[i] -= c[j] * r.Get(i, j)
}
c[i] /= r.Get(i, i)
}
return c, nil
}