Fix usage of gonum

Author: mattn

examples/Matrix_Operations.ipynb

@@ -108,25 +108,25 @@
    ],
    "source": [
     "// Add a and b.\n",
-    "d := mat.NewDense(0, 0, nil)\n",
+    "d := new(mat.Dense)\n",
     "d.Add(a, b)\n",
     "fd := mat.Formatted(d, mat.Prefix(\"            \"))\n",
     "fmt.Printf(\"d = a + b = %0.4v\\n\\n\", fd)\n",
     "\n",
     "// Multiply a and c.\n",
-    "f := mat.NewDense(0, 0, nil)\n",
+    "f := new(mat.Dense)\n",
     "f.Mul(a, c)\n",
     "ff := mat.Formatted(f, mat.Prefix(\"          \"))\n",
     "fmt.Printf(\"f = a c = %0.4v\\n\\n\", ff)\n",
     "\n",
     "// Raising a matrix to a power.\n",
-    "g := mat.NewDense(0, 0, nil)\n",
+    "g := new(mat.Dense)\n",
     "g.Pow(a, 5)\n",
     "fg := mat.Formatted(g, mat.Prefix(\"          \"))\n",
     "fmt.Printf(\"g = a^5 = %0.4v\\n\\n\", fg)\n",
     "\n",
     "// Apply a function to each of the elements of a.\n",
-    "h := mat.NewDense(0, 0, nil)\n",
+    "h := new(mat.Dense)\n",
     "sqrt := func(_, _ int, v float64) float64 { return math.Sqrt(v) }\n",
     "h.Apply(sqrt, a)\n",
     "fh := mat.Formatted(h, mat.Prefix(\"              \"))\n",