Add Laplacian and CrossLaplacian difference functions (#154)

* Add Laplacian and CrossLaplacian difference functions

* use usesOrigin

diff/fd/hessian_test.go

@@ -16,60 +16,62 @@ type HessianTester interface {
 	Hess(dst mat.MutableSymmetric, x []float64)
 }
 
+var hessianTestCases = []struct {
+	h        HessianTester
+	x        []float64
+	settings *Settings
+	tol      float64
+}{
+	{
+		h:   Watson{},
+		x:   []float64{0.2, 0.3, 0.1, 0.4},
+		tol: 1e-3,
+	},
+	{
+		h:   Watson{},
+		x:   []float64{2, 3, 1, 4},
+		tol: 1e-3,
+		settings: &Settings{
+			Step:    1e-5,
+			Formula: Central,
+		},
+	},
+	{
+		h:   Watson{},
+		x:   []float64{2, 3, 1},
+		tol: 1e-3,
+		settings: &Settings{
+			OriginKnown: true,
+			OriginValue: 7606.529501201192,
+		},
+	},
+	{
+		h:   ConstFunc(5),
+		x:   []float64{1, 9},
+		tol: 1e-16,
+	},
+	{
+		h:   LinearFunc{w: []float64{10, 6, -1}, c: 5},
+		x:   []float64{3, 1, 8},
+		tol: 1e-6,
+	},
+	{
+		h: QuadFunc{
+			a: mat.NewSymDense(3, []float64{
+				10, 2, 1,
+				2, 5, -3,
+				1, -3, 6,
+			}),
+			b: mat.NewVecDense(3, []float64{3, -2, -1}),
+			c: 5,
+		},
+		x:   []float64{-1.6, -3, 2},
+		tol: 1e-6,
+	},
+}
+
 func TestHessian(t *testing.T) {
-	for cas, test := range []struct {
-		h        HessianTester
-		x        []float64
-		settings *Settings
-		tol      float64
-	}{
-		{
-			h:   Watson{},
-			x:   []float64{0.2, 0.3, 0.1, 0.4},
-			tol: 1e-3,
-		},
-		{
-			h:   Watson{},
-			x:   []float64{2, 3, 1, 4},
-			tol: 1e-3,
-			settings: &Settings{
-				Step:    1e-5,
-				Formula: Central,
-			},
-		},
-		{
-			h:   Watson{},
-			x:   []float64{2, 3, 1},
-			tol: 1e-3,
-			settings: &Settings{
-				OriginKnown: true,
-				OriginValue: 7606.529501201192,
-			},
-		},
-		{
-			h:   ConstFunc(5),
-			x:   []float64{1, 9},
-			tol: 1e-16,
-		},
-		{
-			h:   LinearFunc{w: []float64{10, 6, -1}, c: 5},
-			x:   []float64{3, 1, 8},
-			tol: 1e-6,
-		},
-		{
-			h: QuadFunc{
-				a: mat.NewSymDense(3, []float64{
-					10, 2, 1,
-					2, 5, -3,
-					1, -3, 6,
-				}),
-				b: mat.NewVecDense(3, []float64{3, -2, -1}),
-				c: 5,
-			},
-			x:   []float64{-1.6, -3, 2},
-			tol: 1e-6,
-		},
-	} {
+	for cas, test := range hessianTestCases {
 		n := len(test.x)
 		got := Hessian(nil, test.h.Func, test.x, test.settings)
 		want := mat.NewSymDense(n, nil)