func polyfit(x, y *matrix.DenseMatrix, n int) *matrix.DenseMatrix {
m := x.Cols()
a := matrix.Zeros(m, n+1)
for i := 0; i < m; i++ {
for j := 0; j <= n; j++ {
a.Set(i, j, math.Pow(x.Get(0, i), float64(j)))
}
}
return lsqr(a, y.Transpose())
}
