Esempio n. 1
0
// Extract real parts, copy them from src to dst.
// In the meanwhile, check if imaginary parts are nearly zero
// and scale the kernel to compensate for unnormalized FFTs.
func scaleRealParts(dst, src *data.Slice, scale float32) {
	util.Argument(2*dst.Len() == src.Len())
	util.Argument(dst.NComp() == 1 && src.NComp() == 1)

	srcList := src.HostCopy().Host()[0]
	dstList := dst.Host()[0]

	// Normally, the FFT'ed kernel is purely real because of symmetry,
	// so we only store the real parts...
	maximg := float32(0.)
	maxreal := float32(0.)
	for i := 0; i < src.Len()/2; i++ {
		dstList[i] = srcList[2*i] * scale
		if fabs(srcList[2*i+0]) > maxreal {
			maxreal = fabs(srcList[2*i+0])
		}
		if fabs(srcList[2*i+1]) > maximg {
			maximg = fabs(srcList[2*i+1])
		}
	}
	// ...however, we check that the imaginary parts are nearly zero,
	// just to be sure we did not make a mistake during kernel creation.
	if maximg/maxreal > FFT_IMAG_TOLERANCE {
		log.Fatalf("Too large FFT kernel imaginary/real part: %v", maximg/maxreal)
	}
}
Esempio n. 2
0
func Image(f *data.Slice, fmin, fmax string) *image.NRGBA {
	dim := f.NComp()
	switch dim {
	default:
		log.Fatalf("unsupported number of components: %v", dim)
	case 3:
		return drawVectors(f.Vectors())
	case 1:
		min, max := extrema(f.Host()[0])
		if fmin != "auto" {
			m, err := strconv.ParseFloat(fmin, 32)
			util.FatalErr(err)
			min = float32(m)
		}
		if fmax != "auto" {
			m, err := strconv.ParseFloat(fmax, 32)
			util.FatalErr(err)
			max = float32(m)
		}
		return drawFloats(f.Scalars(), min, max)
	}
	panic("unreachable")
}