Fix {1,-1,inf,-inf}-norm calculation

The abs should be applied prior to summing elements.

mat64/dense_arithmetic.go

@@ -56,38 +56,38 @@ func (m *Dense) Norm(ord float64) float64 {
 		for i := 0; i < m.mat.Cols; i++ {
 			var s float64
 			for _, e := range m.Col(col, i) {
-				s += e
+				s += math.Abs(e)
 			}
-			n = math.Max(math.Abs(s), n)
+			n = math.Max(s, n)
 		}
 	case math.IsInf(ord, +1):
 		row := make([]float64, m.mat.Cols)
 		for i := 0; i < m.mat.Rows; i++ {
 			var s float64
 			for _, e := range m.Row(row, i) {
-				s += e
+				s += math.Abs(e)
 			}
-			n = math.Max(math.Abs(s), n)
+			n = math.Max(s, n)
 		}
 	case ord == -1:
 		n = math.MaxFloat64
 		col := make([]float64, m.mat.Rows)
 		for i := 0; i < m.mat.Cols; i++ {
 			var s float64
 			for _, e := range m.Col(col, i) {
-				s += e
+				s += math.Abs(e)
 			}
-			n = math.Min(math.Abs(s), n)
+			n = math.Min(s, n)
 		}
 	case math.IsInf(ord, -1):
 		n = math.MaxFloat64
 		row := make([]float64, m.mat.Cols)
 		for i := 0; i < m.mat.Rows; i++ {
 			var s float64
 			for _, e := range m.Row(row, i) {
-				s += e
+				s += math.Abs(e)
 			}
-			n = math.Min(math.Abs(s), n)
+			n = math.Min(s, n)
 		}
 	case ord == 0:
 		for i := 0; i < len(m.mat.Data); i += m.mat.Stride {

mat64/dense_test.go

@@ -592,6 +592,26 @@ func (s *S) TestNorm(c *check.C) {
 			ord:  -inf,
 			norm: 6,
 		},
+		{
+			a:    [][]float64{{1, -2, -2}, {-4, 5, 6}},
+			ord:  1,
+			norm: 8,
+		},
+		{
+			a:    [][]float64{{1, -2, -2}, {-4, 5, 6}},
+			ord:  -1,
+			norm: 5,
+		},
+		{
+			a:    [][]float64{{1, -2, -2}, {-4, 5, 6}},
+			ord:  inf,
+			norm: 15,
+		},
+		{
+			a:    [][]float64{{1, -2, -2}, {-4, 5, 6}},
+			ord:  -inf,
+			norm: 5,
+		},
 	} {
 		a := NewDense(flatten(test.a))
 		c.Check(a.Norm(test.ord), check.Equals, test.norm, check.Commentf("Test %d: %v norm = %f", i, test.a, test.norm))