stat/spatial: use mat.RowNonZeroDoer

stat/spatial/spatial_test.go

@@ -13,7 +13,7 @@ import (
 	"gonum.org/v1/gonum/mat"
 )
 
-func simpleAdjacency(n, wide int, diag bool) *mat.Dense {
+func simpleAdjacency(n, wide int, diag bool) mat.Matrix {
 	m := mat.NewDense(n, n, nil)
 	for i := 0; i < n; i++ {
 		for j := 1; j <= wide; j++ {
@@ -30,11 +30,28 @@ func simpleAdjacency(n, wide int, diag bool) *mat.Dense {
 	return m
 }
 
+func simpleAdjacencyBand(n, wide int, diag bool) mat.Matrix {
+	m := mat.NewBandDense(n, n, wide, wide, nil)
+	for i := 0; i < n; i++ {
+		for j := 1; j <= wide; j++ {
+			if j > i {
+				continue
+			}
+			m.SetBand(i-j, i, 1)
+			m.SetBand(i, i-j, 1)
+		}
+		if diag {
+			m.SetBand(i, i, 1)
+		}
+	}
+	return m
+}
+
 var spatialTests = []struct {
 	from, to float64
 	n, wide  int
 	fn       func(float64, int, *rand.Rand) float64
-	locality func(n, wide int, diag bool) *mat.Dense
+	locality func(n, wide int, diag bool) mat.Matrix
 
 	// Values for MoranI and z-score are obtained from
 	// an R reference implementation.
@@ -46,6 +63,7 @@ var spatialTests = []struct {
 	// of the plotted data.
 	wantSegs int
 }{
+	// Dense matrix locality.
 	{
 		from: 0, to: 1, n: 1000, wide: 1,
 		fn: func(_ float64, _ int, rnd *rand.Rand) float64 {
@@ -122,6 +140,84 @@ var spatialTests = []struct {
 		wantZ:      -31.559531064275987,
 		wantSegs:   0,
 	},
+
+	// Band matrix locality.
+	{
+		from: 0, to: 1, n: 1000, wide: 1,
+		fn: func(_ float64, _ int, rnd *rand.Rand) float64 {
+			return rnd.Float64()
+		},
+		locality: simpleAdjacencyBand,
+
+		wantMoranI: -0.0019631298955953233,
+		wantZ:      -0.03039477405151108,
+		wantSegs:   0,
+	},
+	{
+		from: -math.Pi / 2, to: 3 * math.Pi / 2, n: 1000, wide: 1,
+		fn: func(x float64, _ int, _ *rand.Rand) float64 {
+			y := math.Sin(x)
+			if math.Abs(y) > 0.5 {
+				y *= 1/math.Abs(y) - 1
+			}
+			return y * math.Sin(x*2)
+		},
+		locality: simpleAdjacencyBand,
+
+		wantMoranI: 1.0008149537991464,
+		wantZ:      31.648547078779092,
+		wantSegs:   4,
+	},
+	{
+		from: 0, to: 1, n: 1000, wide: 1,
+		fn: func(_ float64, _ int, rnd *rand.Rand) float64 {
+			return rnd.NormFloat64()
+		},
+		locality: simpleAdjacencyBand,
+
+		wantMoranI: 0.031195199553564902,
+		wantZ:      1.0171161514080056,
+		wantSegs:   0,
+	},
+	{
+		from: 0, to: 1, n: 1000, wide: 1,
+		fn: func(x float64, _ int, rnd *rand.Rand) float64 {
+			if rnd.Float64() < 0.5 {
+				return rnd.NormFloat64() + 5
+			}
+			return rnd.NormFloat64()
+		},
+		locality: simpleAdjacencyBand,
+
+		wantMoranI: -0.016245135637562223,
+		wantZ:      -0.48157993864993476,
+		wantSegs:   0,
+	},
+	{
+		from: 0, to: 1, n: 1000, wide: 1,
+		fn: func(x float64, i int, rnd *rand.Rand) float64 {
+			if i%2 == 0 {
+				return rnd.NormFloat64() + 5
+			}
+			return rnd.NormFloat64()
+		},
+		locality: simpleAdjacencyBand,
+
+		wantMoranI: -0.8565268969272998,
+		wantZ:      -27.027057520918113,
+		wantSegs:   0,
+	},
+	{
+		from: 0, to: 1, n: 1000, wide: 1,
+		fn: func(_ float64, i int, _ *rand.Rand) float64 {
+			return float64(i % 2)
+		},
+		locality: simpleAdjacencyBand,
+
+		wantMoranI: -1,
+		wantZ:      -31.559531064275987,
+		wantSegs:   0,
+	},
 }
 
 func TestGetisOrd(t *testing.T) {