mat: make RowView and ColView return Vector type and add RowViewOf and ColViewOf

Also change Dot signature to accept Vector parameters.

mat/matrix.go

@@ -98,10 +98,10 @@ type Mutable interface {
 	Matrix
 }
 
-// A RowViewer can return a VecDense reflecting a row that is backed by the matrix
-// data. The VecDense returned will have length equal to the number of columns.
+// A RowViewer can return a Vector reflecting a row that is backed by the matrix
+// data. The Vector returned will have length equal to the number of columns.
 type RowViewer interface {
-	RowView(i int) *VecDense
+	RowView(i int) Vector
 }
 
 // A RawRowViewer can return a slice of float64 reflecting a row that is backed by the matrix
@@ -110,10 +110,10 @@ type RawRowViewer interface {
 	RawRowView(i int) []float64
 }
 
-// A ColViewer can return a VecDense reflecting a column that is backed by the matrix
-// data. The VecDense returned will have length equal to the number of rows.
+// A ColViewer can return a Vector reflecting a column that is backed by the matrix
+// data. The Vector returned will have length equal to the number of rows.
 type ColViewer interface {
-	ColView(j int) *VecDense
+	ColView(j int) Vector
 }
 
 // A RawColViewer can return a slice of float64 reflecting a column that is backed by the matrix
@@ -330,13 +330,22 @@ func Det(a Matrix) float64 {
 
 // Dot returns the sum of the element-wise product of a and b.
 // Dot panics if the matrix sizes are unequal.
-func Dot(a, b *VecDense) float64 {
+func Dot(a, b Vector) float64 {
 	la := a.Len()
 	lb := b.Len()
 	if la != lb {
 		panic(ErrShape)
 	}
-	return blas64.Dot(la, a.mat, b.mat)
+	if arv, ok := a.(RawVectorer); ok {
+		if brv, ok := b.(RawVectorer); ok {
+			return blas64.Dot(la, arv.RawVector(), brv.RawVector())
+		}
+	}
+	var sum float64
+	for i := 0; i < la; i++ {
+		sum += a.At(i, 0) * b.At(i, 0)
+	}
+	return sum
 }
 
 // Equal returns whether the matrices a and b have the same size