mat: generalise SymDense RankTwo vector parameters

mat/symmetric.go

@@ -341,27 +341,63 @@ func (s *SymDense) SymOuterK(alpha float64, x Matrix) {
 // RankTwo performs a symmmetric rank-two update to the matrix a and stores
 // the result in the receiver
 //  m = a + alpha * (x * y' + y * x')
-func (s *SymDense) RankTwo(a Symmetric, alpha float64, x, y *VecDense) {
+func (s *SymDense) RankTwo(a Symmetric, alpha float64, x, y Vector) {
 	n := s.mat.N
-	if x.Len() != n {
+	xr, xc := x.Dims()
+	if xr != n || xc != 1 {
 		panic(ErrShape)
 	}
-	if y.Len() != n {
+	yr, yc := y.Dims()
+	if yr != n || yc != 1 {
 		panic(ErrShape)
 	}
-	var w SymDense
-	if s == a {
-		w = *s
-	}
-	w.reuseAs(n)
+
 	if s != a {
 		if rs, ok := a.(RawSymmetricer); ok {
 			s.checkOverlap(generalFromSymmetric(rs.RawSymmetric()))
 		}
-		w.CopySym(a)
 	}
-	blas64.Syr2(alpha, x.mat, y.mat, w.mat)
-	*s = w
+
+	var xmat, ymat blas64.Vector
+	fast := true
+	xU, _ := untranspose(x)
+	if rv, ok := xU.(RawVectorer); ok {
+		xmat = rv.RawVector()
+		s.checkOverlap((&VecDense{mat: xmat, n: x.Len()}).asGeneral())
+	} else {
+		fast = false
+	}
+	yU, _ := untranspose(y)
+	if rv, ok := yU.(RawVectorer); ok {
+		ymat = rv.RawVector()
+		s.checkOverlap((&VecDense{mat: ymat, n: y.Len()}).asGeneral())
+	} else {
+		fast = false
+	}
+
+	if s != a {
+		if rs, ok := a.(RawSymmetricer); ok {
+			s.checkOverlap(generalFromSymmetric(rs.RawSymmetric()))
+		}
+		s.reuseAs(n)
+		s.CopySym(a)
+	}
+
+	if fast {
+		if s != a {
+			s.reuseAs(n)
+			s.CopySym(a)
+		}
+		blas64.Syr2(alpha, xmat, ymat, s.mat)
+		return
+	}
+
+	for i := 0; i < n; i++ {
+		s.reuseAs(n)
+		for j := i; j < n; j++ {
+			s.set(i, j, a.At(i, j)+alpha*(x.AtVec(i)*y.AtVec(j)+y.AtVec(i)*x.AtVec(j)))
+		}
+	}
 }
 
 // ScaleSym multiplies the elements of a by f, placing the result in the receiver.