Add drscl and tests, and fix the dlamch parameters while here.

testlapack/drscl.go

@@ -0,0 +1,48 @@
+package testlapack
+
+import (
+	"math"
+	"testing"
+
+	"github.com/gonum/floats"
+)
+
+type Drscler interface {
+	Drscl(n int, a float64, x []float64, incX int)
+}
+
+func DrsclTest(t *testing.T, impl Drscler) {
+	for _, test := range []struct {
+		x []float64
+		a float64
+	}{
+		{
+			x: []float64{1, 2, 3, 4, 5},
+			a: 4,
+		},
+		{
+			x: []float64{1, 2, 3, 4, 5},
+			a: math.MaxFloat64,
+		},
+		{
+			x: []float64{1, 2, 3, 4, 5},
+			a: 1e-307,
+		},
+	} {
+		xcopy := make([]float64, len(test.x))
+		copy(xcopy, test.x)
+
+		// Cannot test the scaling directly because of floating point scaling issues
+		// (the purpose of Drscl). Instead, check that scaling and scaling back
+		// yeilds approximately x. If overflow or underflow occurs then the scaling
+		// won't match.
+		impl.Drscl(len(test.x), test.a, xcopy, 1)
+		if floats.Equal(xcopy, test.x) {
+			t.Errorf("x unchanged during call to drscl. a = %v, x = %v.", test.a, test.x)
+		}
+		impl.Drscl(len(test.x), 1/test.a, xcopy, 1)
+		if !floats.EqualApprox(xcopy, test.x, 1e-14) {
+			t.Errorf("x not equal after scaling and unscaling. a = %v, x = %v.", test.a, test.x)
+		}
+	}
+}