testlapack: add test for Dlapy2

Closes 210

cgo/lapack_test.go

@@ -76,6 +76,10 @@ func TestDlantr(t *testing.T) {
 	testlapack.DlantrTest(t, impl)
 }
 
+func TestDlapy2(t *testing.T) {
+	testlapack.Dlapy2Test(t, impl)
+}
+
 func TestDlarfx(t *testing.T) {
 	testlapack.DlarfxTest(t, impl)
 }

native/lapack_test.go

@@ -136,6 +136,10 @@ func TestDlange(t *testing.T) {
 	testlapack.DlangeTest(t, impl)
 }
 
+func TestDlapy2(t *testing.T) {
+	testlapack.Dlapy2Test(t, impl)
+}
+
 func TestDlas2(t *testing.T) {
 	testlapack.Dlas2Test(t, impl)
 }

testlapack/dlapy2.go

@@ -0,0 +1,30 @@
+// Copyright ©2016 The gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testlapack
+
+import (
+	"math"
+	"math/rand"
+	"testing"
+
+	"github.com/gonum/floats"
+)
+
+type Dlapy2er interface {
+	Dlapy2(float64, float64) float64
+}
+
+func Dlapy2Test(t *testing.T, impl Dlapy2er) {
+	rnd := rand.New(rand.NewSource(1))
+	for i := 0; i < 10; i++ {
+		x := math.Abs(1e200 * rnd.NormFloat64())
+		y := math.Abs(1e200 * rnd.NormFloat64())
+		got := impl.Dlapy2(x, y)
+		want := math.Hypot(x, y)
+		if !floats.EqualWithinRel(got, want, 1e-16) {
+			t.Errorf("Dlapy2(%g, %g) = %g, want %g", x, y, got, want)
+		}
+	}
+}