dsp/window: add Values.TransformTo window functions and example

dsp/window/window_example_test.go

@@ -118,3 +118,42 @@ func ExampleValues() {
 	//
 	// dst: [0.000000 0.164595 0.324699 0.475947 0.614213 0.735724 0.837166 0.915773 0.969400 0.996584 0.996584 0.969400 0.915773 0.837166 0.735724 0.614213 0.475947 0.324699 0.164595 0.000000]
 }
+
+func ExampleValues_TransformTo_gabor() {
+	src := []float64{1, 2, 1, 0, -1, -1, -2, -2, -1, -1,
+		0, 1, 1, 2, 1, 0, -1, -2, -1, 0}
+
+	// Create a Gaussian Window lookup table for 4 samples.
+	gaussian := window.NewValues(window.Gaussian{0.5}.Transform, 4)
+
+	// Prepare a destination.
+	dst := make([]float64, 8)
+
+	// Apply the transformation to the src, placing it in dst.
+	for i := 0; i < len(src)-len(gaussian); i++ {
+		gaussian.TransformTo(dst[0:len(gaussian)], src[i:i+len(gaussian)])
+
+		// To perform the Gabor transform, we would calculate
+		// the FFT on dst for each iteration.
+		fmt.Printf("FFT(%f)\n", dst)
+	}
+
+	// Output:
+	//
+	// FFT([0.135335 1.601475 0.800737 0.000000 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.270671 0.800737 0.000000 -0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.135335 0.000000 -0.800737 -0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.000000 -0.800737 -0.800737 -0.270671 0.000000 0.000000 0.000000 0.000000])
+	// FFT([-0.135335 -0.800737 -1.601475 -0.270671 0.000000 0.000000 0.000000 0.000000])
+	// FFT([-0.135335 -1.601475 -1.601475 -0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([-0.270671 -1.601475 -0.800737 -0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([-0.270671 -0.800737 -0.800737 0.000000 0.000000 0.000000 0.000000 0.000000])
+	// FFT([-0.135335 -0.800737 0.000000 0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([-0.135335 0.000000 0.800737 0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.000000 0.800737 0.800737 0.270671 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.135335 0.800737 1.601475 0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.135335 1.601475 0.800737 0.000000 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.270671 0.800737 0.000000 -0.135335 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.135335 0.000000 -0.800737 -0.270671 0.000000 0.000000 0.000000 0.000000])
+	// FFT([0.000000 -0.800737 -1.601475 -0.135335 0.000000 0.000000 0.000000 0.000000])
+}

dsp/window/window_parametric.go

@@ -147,6 +147,24 @@ func (v Values) Transform(seq []float64) []float64 {
 	return seq
 }
 
+// TransformTo applies the weights in the receiver to src placing the result
+// in dst. If v is nil, TransformTo is a no-op, otherwise the length of v must
+// match the length of src and dst.
+func (v Values) TransformTo(dst, src []float64) {
+	if v == nil {
+		return
+	}
+	if len(v) != len(src) {
+		panic("window: seq length mismatch")
+	}
+	if len(v) != len(dst) {
+		panic("window: dst length mismatch")
+	}
+	for i, w := range v {
+		dst[i] = w * src[i]
+	}
+}
+
 // TransformComplex applies the weights in the receiver to seq in place, returning
 // the result. If v is nil, TransformComplex is a no-op, otherwise the length of v
 // must match the length of seq.
@@ -163,3 +181,22 @@ func (v Values) TransformComplex(seq []complex128) []complex128 {
 	}
 	return seq
 }
+
+// TransformComplexTo applies the weights in the receiver to src placing the
+// result in dst. If v is nil, TransformComplexTo is a no-op, otherwise the
+// length of v must match the length of src and dst.
+func (v Values) TransformComplexTo(dst, src []complex128) {
+	if v == nil {
+		return
+	}
+	if len(v) != len(src) {
+		panic("window: seq length mismatch")
+	}
+	if len(v) != len(dst) {
+		panic("window: dst length mismatch")
+	}
+	for i, w := range v {
+		sv := src[i]
+		dst[i] = complex(w*real(sv), w*imag(sv))
+	}
+}

dsp/window/window_test.go

@@ -174,7 +174,18 @@ func TestWindows(t *testing.T) {
 				src[i] = 1
 			}
 
-			dst = NewValues(test.fn, len(src)).Transform(src)
+			vals := NewValues(test.fn, len(src))
+			dst = vals.Transform(src)
+			if !floats.EqualApprox(dst, test.want, tol) {
+				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
+			}
+
+			for i := range src {
+				src[i] = 1
+			}
+
+			dst = make([]float64, len(src))
+			vals.TransformTo(dst, src)
 			if !floats.EqualApprox(dst, test.want, tol) {
 				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
 			}
@@ -202,7 +213,18 @@ func TestWindowsComplex(t *testing.T) {
 				src[i] = complex(1, 1)
 			}
 
-			dst = NewValues(test.fn, len(src)).TransformComplex(src)
+			vals := NewValues(test.fn, len(src))
+			dst = vals.TransformComplex(src)
+			if !equalApprox(dst, test.want, tol) {
+				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
+			}
+
+			for i := range src {
+				src[i] = complex(1, 1)
+			}
+
+			dst = make([]complex128, len(src))
+			vals.TransformComplexTo(dst, src)
 			if !equalApprox(dst, test.want, tol) {
 				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
 			}