mat: provide internal slice methods that returns the concrete types

mat/cholesky_test.go

@@ -505,7 +505,7 @@ func TestCholeskyExtendVecSym(t *testing.T) {
 		},
 	} {
 		n := test.a.Symmetric()
-		as := test.a.SliceSym(0, n-1).(*SymDense)
+		as := test.a.sliceSym(0, n-1)
 
 		// Compute the full factorization to use later (do the full factorization
 		// first to ensure the matrix is positive definite).

mat/dense.go

@@ -318,6 +318,10 @@ func (m *Dense) DiagView() Diagonal {
 // Slice panics with ErrIndexOutOfRange if the slice is outside the capacity
 // of the receiver.
 func (m *Dense) Slice(i, k, j, l int) Matrix {
+	return m.slice(i, k, j, l)
+}
+
+func (m *Dense) slice(i, k, j, l int) *Dense {
 	mr, mc := m.Caps()
 	if i < 0 || mr <= i || j < 0 || mc <= j || k < i || mr < k || l < j || mc < l {
 		if i == k || j == l {
@@ -545,7 +549,7 @@ func (m *Dense) Stack(a, b Matrix) {
 	m.reuseAsNonZeroed(ar+br, ac)
 
 	m.Copy(a)
-	w := m.Slice(ar, ar+br, 0, bc).(*Dense)
+	w := m.slice(ar, ar+br, 0, bc)
 	w.Copy(b)
 }
 
@@ -563,7 +567,7 @@ func (m *Dense) Augment(a, b Matrix) {
 	m.reuseAsNonZeroed(ar, ac+bc)
 
 	m.Copy(a)
-	w := m.Slice(0, br, ac, ac+bc).(*Dense)
+	w := m.slice(0, br, ac, ac+bc)
 	w.Copy(b)
 }
 

mat/dense_arithmetic.go

@@ -682,7 +682,7 @@ func (m *Dense) Kronecker(a, b Matrix) {
 	m.reuseAsNonZeroed(ra*rb, ca*cb)
 	for i := 0; i < ra; i++ {
 		for j := 0; j < ca; j++ {
-			m.Slice(i*rb, (i+1)*rb, j*cb, (j+1)*cb).(*Dense).Scale(a.At(i, j), b)
+			m.slice(i*rb, (i+1)*rb, j*cb, (j+1)*cb).Scale(a.At(i, j), b)
 		}
 	}
 }

mat/gsvd.go

@@ -265,16 +265,14 @@ func (gsvd *GSVD) ZeroRTo(dst *Dense) {
 		capRows: r,
 		capCols: c,
 	}
-	dst.Slice(0, h, c-k-l, c).(*Dense).
-		Copy(a.Slice(0, h, c-k-l, c))
+	dst.slice(0, h, c-k-l, c).Copy(a.Slice(0, h, c-k-l, c))
 	if r < k+l {
 		b := Dense{
 			mat:     gsvd.b,
 			capRows: gsvd.p,
 			capCols: c,
 		}
-		dst.Slice(r, k+l, c+r-k-l, c).(*Dense).
-			Copy(b.Slice(r-k, l, c+r-k-l, c))
+		dst.slice(r, k+l, c+r-k-l, c).Copy(b.Slice(r-k, l, c+r-k-l, c))
 	}
 }
 

mat/symmetric.go

@@ -563,6 +563,10 @@ func (s *SymDense) SubsetSym(a Symmetric, set []int) {
 // SliceSym panics with ErrIndexOutOfRange if the slice is outside the
 // capacity of the receiver.
 func (s *SymDense) SliceSym(i, k int) Symmetric {
+	return s.sliceSym(i, k)
+}
+
+func (s *SymDense) sliceSym(i, k int) *SymDense {
 	sz := s.cap
 	if i < 0 || sz < i || k < i || sz < k {
 		panic(ErrIndexOutOfRange)

mat/symmetric_test.go

@@ -608,7 +608,7 @@ func TestViewGrowSquare(t *testing.T) {
 		// Take a subset and check the view matches.
 		start1 := test.start1
 		span1 := test.span1
-		v := s.SliceSym(start1, start1+span1).(*SymDense)
+		v := s.sliceSym(start1, start1+span1)
 		for i := 0; i < span1; i++ {
 			for j := i; j < span1; j++ {
 				if v.At(i, j) != s.At(start1+i, start1+j) {