func FFT_aux(this, xr, RowTemp *Matrix.Matrix, N, skip int, tf *[]complex128) {
if N == 1 {
xr.SetRow(1, this.GetReferenceRow(1))
return
}
FFT_aux(this, xr, RowTemp, N/2, skip*2, tf)
FFT_aux(this.MatrixWithoutFirstRows(skip), xr.MatrixWithoutFirstRows(N/2), RowTemp, N/2, skip*2, tf)
for k := 0; k < N/2; k++ {
xr.ScalarRowIntoRowMatrix(RowTemp, k+1+N/2, (*tf)[k*skip])
sr, rr, _ := Matrix.Sum_Sustract(xr.GetReferenceRow(k+1), RowTemp)
xr.SetRow(k+1, sr)
xr.SetRow(k+1+N/2, rr)
}
}