Add flat top window

window/window.go

@@ -96,3 +96,39 @@ func Bartlett(L int) []float64 {
 
 	return r
 }
+
+// FlatTop returns an L-point flat top window.
+// Reference: http://www.mathworks.com/help/signal/ref/flattopwin.html
+func FlatTop(L int) []float64 {
+	const (
+		alpha0 = float64(0.21557895)
+		alpha1 = float64(0.41663158)
+		alpha2 = float64(0.277263158)
+		alpha3 = float64(0.083578947)
+		alpha4 = float64(0.006947368)
+	)
+
+	r := make([]float64, L)
+
+	if L == 1 {
+		r[0] = 1
+		return r
+	}
+
+	N := L - 1
+	coef := 2 * math.Pi / float64(N)
+
+	for n := 0; n <= N; n++ {
+		factor := float64(n) * coef
+
+		term0 := alpha0
+		term1 := alpha1 * math.Cos(factor)
+		term2 := alpha2 * math.Cos(2*factor)
+		term3 := alpha3 * math.Cos(3*factor)
+		term4 := alpha4 * math.Cos(4*factor)
+
+		r[n] = term0 - term1 + term2 - term3 + term4
+	}
+
+	return r
+}

window/window_test.go

@@ -27,6 +27,7 @@ type windowTest struct {
 	hamming  []float64
 	hann     []float64
 	bartlett []float64
+	flatTop  []float64
 }
 
 var windowTests = []windowTest{
@@ -35,18 +36,21 @@ var windowTests = []windowTest{
 		[]float64{1},
 		[]float64{1},
 		[]float64{1},
+		[]float64{1},
 	},
 	{
 		5,
 		[]float64{0.08, 0.54, 1, 0.54, 0.08},
 		[]float64{0, 0.5, 1, 0.5, 0},
 		[]float64{0, 0.5, 1, 0.5, 0},
+		[]float64{-0.0004210510000000013, -0.05473684000000003, 1, -0.05473684000000003, -0.0004210510000000013},
 	},
 	{
 		10,
 		[]float64{0.08, 0.18761956, 0.46012184, 0.77, 0.97225861, 0.97225861, 0.77, 0.46012184, 0.18761956, 0.08},
 		[]float64{0, 0.116977778440511, 0.413175911166535, 0.75, 0.969846310392954, 0.969846310392954, 0.75, 0.413175911166535, 0.116977778440511, 0},
 		[]float64{0, 0.222222222222222, 0.444444444444444, 0.666666666666667, 0.888888888888889, 0.888888888888889, 0.666666666666667, 0.444444444444444, 0.222222222222222, 0},
+		[]float64{-0.000421051000000, -0.020172031509486, -0.070199042063189, 0.198210530000000, 0.862476344072674, 0.862476344072674, 0.198210530000000, -0.070199042063189, -0.020172031509486, -0.000421051000000},
 	},
 }
 
@@ -72,5 +76,10 @@ func TestWindowFunctions(t *testing.T) {
 		if !dsputils.PrettyClose(o, v.hamming) {
 			t.Error("apply error\noutput:", o, "\nexpected:", v.hamming)
 		}
+
+		o = FlatTop(v.in)
+		if !dsputils.PrettyClose(o, v.flatTop) {
+			t.Error("flatTop error\ninput:", v.in, "\noutput:", o, "\nexpected:", v.flatTop)
+		}
 	}
 }