mat: change factorization inputs to use bit types (#872)

* mat: change factorization inputs to use bit types

Fixes #756 and #748.

mat/consts.go

@@ -13,42 +13,3 @@ const (
 	// Lower specifies a lower triangular matrix.
 	Lower TriKind = false
 )
-
-// SVDKind specifies the treatment of singular vectors during an SVD
-// factorization.
-type SVDKind int
-
-const (
-	// SVDNone specifies that no singular vectors should be computed during
-	// the decomposition.
-	SVDNone SVDKind = iota + 1
-	// SVDThin computes the thin singular vectors, that is, it computes
-	//  A = U~ * Σ * V~^T
-	// where U~ is of size m×min(m,n), Σ is a diagonal matrix of size min(m,n)×min(m,n)
-	// and V~ is of size n×min(m,n).
-	SVDThin
-	// SVDFull computes the full singular value decomposition,
-	//  A = U * Σ * V^T
-	// where U is of size m×m, Σ is an m×n diagonal matrix, and V is an n×n matrix.
-	SVDFull
-)
-
-// GSVDKind specifies the treatment of singular vectors during a GSVD
-// factorization.
-type GSVDKind int
-
-const (
-	// GSVDU specifies that the U singular vectors should be computed during
-	// the decomposition.
-	GSVDU GSVDKind = 1 << iota
-	// GSVDV specifies that the V singular vectors should be computed during
-	// the decomposition.
-	GSVDV
-	// GSVDQ specifies that the Q singular vectors should be computed during
-	// the decomposition.
-	GSVDQ
-
-	// GSVDNone specifies that no singular vector should be computed during
-	// the decomposition.
-	GSVDNone
-)

mat/eigen.go

@@ -104,12 +104,25 @@ func (m *Dense) EigenvectorsSym(e *EigenSym) {
 	m.Copy(e.vectors)
 }
 
+// EigenKind specifies the computation of eigenvectors during factorization.
+type EigenKind int
+
+const (
+	// EigenNone specifies to not compute any eigenvectors.
+	EigenNone EigenKind = 0
+	// EigenLeft specifies to compute the left eigenvectors.
+	EigenLeft EigenKind = 1 << iota
+	// EigenRight specifies to compute the right eigenvectors.
+	EigenRight
+	// EigenBoth is a convenience value for computing both eigenvectors.
+	EigenBoth EigenKind = EigenLeft | EigenRight
+)
+
 // Eigen is a type for creating and using the eigenvalue decomposition of a dense matrix.
 type Eigen struct {
 	n int // The size of the factorized matrix.
 
-	right bool // have the right eigenvectors been computed
-	left  bool // have the left eigenvectors been computed
+	kind EigenKind
 
 	values   []complex128
 	rVectors *CDense
@@ -118,7 +131,7 @@ type Eigen struct {
 
 // succFact returns whether the receiver contains a successful factorization.
 func (e *Eigen) succFact() bool {
-	return len(e.values) != 0
+	return e.n != 0
 }
 
 // Factorize computes the eigenvalues of the square matrix a, and optionally
@@ -135,13 +148,17 @@ func (e *Eigen) succFact() bool {
 //
 // Typically eigenvectors refer to right eigenvectors.
 //
-// In all cases, Factorize computes the eigenvalues of the matrix. If right and left
-// are true, then the right and left eigenvectors will be computed, respectively.
+// In all cases, Factorize computes the eigenvalues of the matrix. kind
+// specifies which of the eigenvectors, if any, to compute. See the EigenKind
+// documentation for more information.
 // Eigen panics if the input matrix is not square.
 //
 // Factorize returns whether the decomposition succeeded. If the decomposition
 // failed, methods that require a successful factorization will panic.
-func (e *Eigen) Factorize(a Matrix, left, right bool) (ok bool) {
+func (e *Eigen) Factorize(a Matrix, kind EigenKind) (ok bool) {
+	// kill previous factorization.
+	e.n = 0
+	e.kind = 0
 	// Copy a because it is modified during the Lapack call.
 	r, c := a.Dims()
 	if r != c {
@@ -150,6 +167,9 @@ func (e *Eigen) Factorize(a Matrix, left, right bool) (ok bool) {
 	var sd Dense
 	sd.Clone(a)
 
+	left := kind&EigenLeft != 0
+	right := kind&EigenRight != 0
+
 	var vl, vr Dense
 	jobvl := lapack.LeftEVNone
 	jobvr := lapack.RightEVNone
@@ -183,8 +203,7 @@ func (e *Eigen) Factorize(a Matrix, left, right bool) (ok bool) {
 		return false
 	}
 	e.n = r
-	e.right = right
-	e.left = left
+	e.kind = kind
 
 	// Construct complex eigenvalues from float64 data.
 	values := make([]complex128, r)
@@ -212,6 +231,15 @@ func (e *Eigen) Factorize(a Matrix, left, right bool) (ok bool) {
 	return true
 }
 
+// Kind returns the EigenKind of the decomposition. If no decomposition has been
+// computed, Kind returns -1.
+func (e *Eigen) Kind() EigenKind {
+	if !e.succFact() {
+		return -1
+	}
+	return e.kind
+}
+
 // Values extracts the eigenvalues of the factorized matrix. If dst is
 // non-nil, the values are stored in-place into dst. In this case
 // dst must have length n, otherwise Values will panic. If dst is
@@ -281,7 +309,7 @@ func (e *Eigen) VectorsTo(dst *CDense) *CDense {
 	if !e.succFact() {
 		panic(badFact)
 	}
-	if !e.right {
+	if e.kind&EigenRight == 0 {
 		panic(badNoVect)
 	}
 	if dst == nil {
@@ -303,7 +331,7 @@ func (e *Eigen) LeftVectorsTo(dst *CDense) *CDense {
 	if !e.succFact() {
 		panic(badFact)
 	}
-	if !e.left {
+	if e.kind&EigenLeft == 0 {
 		panic(badNoVect)
 	}
 	if dst == nil {

mat/eigen_example_test.go

@@ -50,7 +50,7 @@ func ExampleEigen() {
 	fmt.Printf("A = %v\n\n", mat.Formatted(a, mat.Prefix("    ")))
 
 	var eig mat.Eigen
-	ok := eig.Factorize(a, true, false)
+	ok := eig.Factorize(a, mat.EigenLeft)
 	if !ok {
 		log.Fatal("Eigendecomposition failed")
 	}

mat/eigen_test.go

@@ -63,13 +63,13 @@ func TestEigen(t *testing.T) {
 		},
 	} {
 		var e1, e2, e3, e4 Eigen
-		ok := e1.Factorize(test.a, true, true)
+		ok := e1.Factorize(test.a, EigenBoth)
 		if !ok {
 			panic("bad factorization")
 		}
-		e2.Factorize(test.a, false, true)
-		e3.Factorize(test.a, true, false)
-		e4.Factorize(test.a, false, false)
+		e2.Factorize(test.a, EigenRight)
+		e3.Factorize(test.a, EigenLeft)
+		e4.Factorize(test.a, EigenNone)
 
 		v1 := e1.Values(nil)
 		if !cmplxEqualTol(v1, test.values, 1e-14) {

mat/gsvd.go

@@ -11,6 +11,29 @@ import (
 	"gonum.org/v1/gonum/lapack/lapack64"
 )
 
+// GSVDKind specifies the treatment of singular vectors during a GSVD
+// factorization.
+type GSVDKind int
+
+const (
+	// GSVDNone specifies that no singular vectors should be computed during
+	// the decomposition.
+	GSVDNone GSVDKind = 0
+
+	// GSVDU specifies that the U singular vectors should be computed during
+	// the decomposition.
+	GSVDU GSVDKind = 1 << iota
+	// GSVDV specifies that the V singular vectors should be computed during
+	// the decomposition.
+	GSVDV
+	// GSVDQ specifies that the Q singular vectors should be computed during
+	// the decomposition.
+	GSVDQ
+
+	// GSVDAll is a convenience value for computing all of the singular vectors.
+	GSVDAll = GSVDU | GSVDV | GSVDQ
+)
+
 // GSVD is a type for creating and using the Generalized Singular Value Decomposition
 // (GSVD) of a matrix.
 //
@@ -28,12 +51,17 @@ type GSVD struct {
 	iwork []int
 }
 
+// succFact returns whether the receiver contains a successful factorization.
+func (gsvd *GSVD) succFact() bool {
+	return gsvd.r != 0
+}
+
 // Factorize computes the generalized singular value decomposition (GSVD) of the input
 // the r×c matrix A and the p×c matrix B. The singular values of A and B are computed
 // in all cases, while the singular vectors are optionally computed depending on the
 // input kind.
 //
-// The full singular value decomposition (kind == GSVDU|GSVDV|GSVDQ) deconstructs A and B as
+// The full singular value decomposition (kind == GSVDAll) deconstructs A and B as
 //  A = U * Σ₁ * [ 0 R ] * Q^T
 //
 //  B = V * Σ₂ * [ 0 R ] * Q^T
@@ -49,6 +77,10 @@ type GSVD struct {
 // Factorize returns whether the decomposition succeeded. If the decomposition
 // failed, routines that require a successful factorization will panic.
 func (gsvd *GSVD) Factorize(a, b Matrix, kind GSVDKind) (ok bool) {
+	// kill the previous decomposition
+	gsvd.r = 0
+	gsvd.kind = 0
+
 	r, c := a.Dims()
 	gsvd.r, gsvd.c = r, c
 	p, c := b.Dims()
@@ -64,7 +96,7 @@ func (gsvd *GSVD) Factorize(a, b Matrix, kind GSVDKind) (ok bool) {
 		jobU = lapack.GSVDNone
 		jobV = lapack.GSVDNone
 		jobQ = lapack.GSVDNone
-	case (GSVDU|GSVDV|GSVDQ)&kind != 0:
+	case GSVDAll&kind != 0:
 		if GSVDU&kind != 0 {
 			jobU = lapack.GSVDU
 			gsvd.u = blas64.General{
@@ -115,9 +147,12 @@ func (gsvd *GSVD) Factorize(a, b Matrix, kind GSVDKind) (ok bool) {
 	return ok
 }
 
-// Kind returns the matrix.GSVDKind of the decomposition. If no decomposition has been
-// computed, Kind returns 0.
+// Kind returns the GSVDKind of the decomposition. If no decomposition has been
+// computed, Kind returns -1.
 func (gsvd *GSVD) Kind() GSVDKind {
+	if !gsvd.succFact() {
+		return -1
+	}
 	return gsvd.kind
 }
 
@@ -134,8 +169,8 @@ func (gsvd *GSVD) Rank() (k, l int) {
 //
 // GeneralizedValues will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) GeneralizedValues(v []float64) []float64 {
-	if gsvd.kind == 0 {
-		panic("gsvd: no decomposition computed")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	r := gsvd.r
 	c := gsvd.c
@@ -159,8 +194,8 @@ func (gsvd *GSVD) GeneralizedValues(v []float64) []float64 {
 //
 // ValuesA will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) ValuesA(s []float64) []float64 {
-	if gsvd.kind == 0 {
-		panic("gsvd: no decomposition computed")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	r := gsvd.r
 	c := gsvd.c
@@ -184,8 +219,8 @@ func (gsvd *GSVD) ValuesA(s []float64) []float64 {
 //
 // ValuesB will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) ValuesB(s []float64) []float64 {
-	if gsvd.kind == 0 {
-		panic("gsvd: no decomposition computed")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	r := gsvd.r
 	c := gsvd.c
@@ -207,8 +242,8 @@ func (gsvd *GSVD) ValuesB(s []float64) []float64 {
 //
 // ZeroRTo will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) ZeroRTo(dst *Dense) *Dense {
-	if gsvd.kind == 0 {
-		panic("gsvd: no decomposition computed")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	r := gsvd.r
 	c := gsvd.c
@@ -245,8 +280,8 @@ func (gsvd *GSVD) ZeroRTo(dst *Dense) *Dense {
 //
 // SigmaATo will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) SigmaATo(dst *Dense) *Dense {
-	if gsvd.kind == 0 {
-		panic("gsvd: no decomposition computed")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	r := gsvd.r
 	k := gsvd.k
@@ -271,8 +306,8 @@ func (gsvd *GSVD) SigmaATo(dst *Dense) *Dense {
 //
 // SigmaBTo will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) SigmaBTo(dst *Dense) *Dense {
-	if gsvd.kind == 0 {
-		panic("gsvd: no decomposition computed")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	r := gsvd.r
 	p := gsvd.p
@@ -298,6 +333,9 @@ func (gsvd *GSVD) SigmaBTo(dst *Dense) *Dense {
 //
 // UTo will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) UTo(dst *Dense) *Dense {
+	if !gsvd.succFact() {
+		panic(badFact)
+	}
 	if gsvd.kind&GSVDU == 0 {
 		panic("mat: improper GSVD kind")
 	}
@@ -324,6 +362,9 @@ func (gsvd *GSVD) UTo(dst *Dense) *Dense {
 //
 // VTo will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) VTo(dst *Dense) *Dense {
+	if !gsvd.succFact() {
+		panic(badFact)
+	}
 	if gsvd.kind&GSVDV == 0 {
 		panic("mat: improper GSVD kind")
 	}
@@ -350,6 +391,9 @@ func (gsvd *GSVD) VTo(dst *Dense) *Dense {
 //
 // QTo will panic if the receiver does not contain a successful factorization.
 func (gsvd *GSVD) QTo(dst *Dense) *Dense {
+	if !gsvd.succFact() {
+		panic(badFact)
+	}
 	if gsvd.kind&GSVDQ == 0 {
 		panic("mat: improper GSVD kind")
 	}

mat/hogsvd.go

@@ -24,6 +24,11 @@ type HOGSVD struct {
 	err error
 }
 
+// succFact returns whether the receiver contains a successful factorization.
+func (gsvd *HOGSVD) succFact() bool {
+	return gsvd.n != 0
+}
+
 // Factorize computes the higher order generalized singular value decomposition (HOGSVD)
 // of the n input r_i×c column tall matrices in m. HOGSV extends the GSVD case from 2 to n
 // input matrices.
@@ -96,7 +101,7 @@ func (gsvd *HOGSVD) Factorize(m ...Matrix) (ok bool) {
 	s.Scale(1/float64(len(m)*(len(m)-1)), s)
 
 	var eig Eigen
-	ok = eig.Factorize(s.T(), false, true)
+	ok = eig.Factorize(s.T(), EigenRight)
 	if !ok {
 		gsvd.err = errors.New("hogsvd: eigen decomposition failed")
 		return false
@@ -157,8 +162,8 @@ func (gsvd *HOGSVD) Len() int {
 //
 // UTo will panic if the receiver does not contain a successful factorization.
 func (gsvd *HOGSVD) UTo(dst *Dense, n int) *Dense {
-	if gsvd.n == 0 {
-		panic("hogsvd: unsuccessful factorization")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	if n < 0 || gsvd.n <= n {
 		panic("hogsvd: invalid index")
@@ -187,8 +192,8 @@ func (gsvd *HOGSVD) UTo(dst *Dense, n int) *Dense {
 //
 // Values will panic if the receiver does not contain a successful factorization.
 func (gsvd *HOGSVD) Values(s []float64, n int) []float64 {
-	if gsvd.n == 0 {
-		panic("hogsvd: unsuccessful factorization")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	if n < 0 || gsvd.n <= n {
 		panic("hogsvd: invalid index")
@@ -214,8 +219,8 @@ func (gsvd *HOGSVD) Values(s []float64, n int) []float64 {
 //
 // VTo will panic if the receiver does not contain a successful factorization.
 func (gsvd *HOGSVD) VTo(dst *Dense) *Dense {
-	if gsvd.n == 0 {
-		panic("hogsvd: unsuccessful factorization")
+	if !gsvd.succFact() {
+		panic(badFact)
 	}
 	if dst == nil {
 		r, c := gsvd.v.Dims()

mat/svd.go

@@ -20,6 +20,35 @@ type SVD struct {
 	vt blas64.General
 }
 
+// SVDKind specifies the treatment of singular vectors during an SVD
+// factorization.
+type SVDKind int
+
+const (
+	// SVDNone specifies that no singular vectors should be computed during
+	// the decomposition.
+	SVDNone SVDKind = 0
+
+	// SVDThinU specifies the thin decomposition for U should be computed.
+	SVDThinU SVDKind = 1 << (iota - 1)
+	// SVDFullU specifies the full decomposition for U should be computed.
+	SVDFullU
+	// SVDThinV specifies the thin decomposition for V should be computed.
+	SVDThinV
+	// SVDFullV specifies the full decomposition for V should be computed.
+	SVDFullV
+
+	// SVDThin is a convenience value for computing both thin vectors.
+	SVDThin SVDKind = SVDThinU | SVDThinV
+	// SVDThin is a convenience value for computing both full vectors.
+	SVDFull SVDKind = SVDFullU | SVDFullV
+)
+
+// succFact returns whether the receiver contains a successful factorization.
+func (svd *SVD) succFact() bool {
+	return len(svd.s) != 0
+}
+
 // Factorize computes the singular value decomposition (SVD) of the input matrix A.
 // The singular values of A are computed in all cases, while the singular
 // vectors are optionally computed depending on the input kind.
@@ -32,61 +61,67 @@ type SVD struct {
 // The first min(m,n) columns of U and V are, respectively, the left and right
 // singular vectors of A.
 //
-// It is frequently not necessary to compute the full SVD. Computation time and
-// storage costs can be reduced using the appropriate kind. Only the singular
-// values can be computed (kind == SVDNone), or a "thin" representation of the
-// orthogonal matrices U and V (kind = SVDThin). The thin representation can
-// save a significant amount of memory if m >> n or m << n.
+// Significant storage space can be saved by using the thin representation of
+// the SVD (kind == SVDThin) instead of the full SVD, especially if
+// m >> n or m << n. The thin SVD finds
+//  A = U~ * Σ * V~^T
+// where U~ is of size m×min(m,n), Σ is a diagonal matrix of size min(m,n)×min(m,n)
+// and V~ is of size n×min(m,n).
 //
 // Factorize returns whether the decomposition succeeded. If the decomposition
 // failed, routines that require a successful factorization will panic.
 func (svd *SVD) Factorize(a Matrix, kind SVDKind) (ok bool) {
+	// kill previous factorization
+	svd.s = svd.s[:0]
+	svd.kind = kind
+
 	m, n := a.Dims()
 	var jobU, jobVT lapack.SVDJob
-	switch kind {
-	default:
-		panic("svd: bad input kind")
-	case SVDNone:
-		svd.u.Stride = 1
-		svd.vt.Stride = 1
-		jobU = lapack.SVDNone
-		jobVT = lapack.SVDNone
-	case SVDFull:
-		// TODO(btracey): This code should be modified to have the smaller
-		// matrix written in-place into aCopy when the lapack/native/dgesvd
-		// implementation is complete.
+
+	// TODO(btracey): This code should be modified to have the smaller
+	// matrix written in-place into aCopy when the lapack/native/dgesvd
+	// implementation is complete.
+	switch {
+	case kind&SVDFullU != 0:
+		jobU = lapack.SVDAll
 		svd.u = blas64.General{
 			Rows:   m,
 			Cols:   m,
 			Stride: m,
 			Data:   use(svd.u.Data, m*m),
 		}
-		svd.vt = blas64.General{
-			Rows:   n,
-			Cols:   n,
-			Stride: n,
-			Data:   use(svd.vt.Data, n*n),
-		}
-		jobU = lapack.SVDAll
-		jobVT = lapack.SVDAll
-	case SVDThin:
-		// TODO(btracey): This code should be modified to have the larger
-		// matrix written in-place into aCopy when the lapack/native/dgesvd
-		// implementation is complete.
+	case kind&SVDThinU != 0:
+		jobU = lapack.SVDStore
 		svd.u = blas64.General{
 			Rows:   m,
 			Cols:   min(m, n),
 			Stride: min(m, n),
 			Data:   use(svd.u.Data, m*min(m, n)),
 		}
+	default:
+		svd.u.Stride = 1
+		jobU = lapack.SVDNone
+	}
+	switch {
+	case kind&SVDFullV != 0:
+		svd.vt = blas64.General{
+			Rows:   n,
+			Cols:   n,
+			Stride: n,
+			Data:   use(svd.vt.Data, n*n),
+		}
+		jobVT = lapack.SVDAll
+	case kind&SVDThinV != 0:
 		svd.vt = blas64.General{
 			Rows:   min(m, n),
 			Cols:   n,
 			Stride: n,
 			Data:   use(svd.vt.Data, min(m, n)*n),
 		}
-		jobU = lapack.SVDStore
 		jobVT = lapack.SVDStore
+	default:
+		svd.vt.Stride = 1
+		jobVT = lapack.SVDNone
 	}
 
 	// A is destroyed on call, so copy the matrix.
@@ -105,17 +140,20 @@ func (svd *SVD) Factorize(a Matrix, kind SVDKind) (ok bool) {
 	return ok
 }
 
-// Kind returns the matrix.SVDKind of the decomposition. If no decomposition has been
-// computed, Kind returns 0.
+// Kind returns the SVDKind of the decomposition. If no decomposition has been
+// computed, Kind returns -1.
 func (svd *SVD) Kind() SVDKind {
+	if !svd.succFact() {
+		return -1
+	}
 	return svd.kind
 }
 
 // Cond returns the 2-norm condition number for the factorized matrix. Cond will
 // panic if the receiver does not contain a successful factorization.
 func (svd *SVD) Cond() float64 {
-	if svd.kind == 0 {
-		panic("svd: no decomposition computed")
+	if !svd.succFact() {
+		panic(badFact)
 	}
 	return svd.s[0] / svd.s[len(svd.s)-1]
 }
@@ -129,8 +167,8 @@ func (svd *SVD) Cond() float64 {
 //
 // Values will panic if the receiver does not contain a successful factorization.
 func (svd *SVD) Values(s []float64) []float64 {
-	if svd.kind == 0 {
-		panic("svd: no decomposition computed")
+	if !svd.succFact() {
+		panic(badFact)
 	}
 	if s == nil {
 		s = make([]float64, len(svd.s))
@@ -147,13 +185,16 @@ func (svd *SVD) Values(s []float64) []float64 {
 // values as returned from SVD.Values.
 //
 // If dst is not nil, U is stored in-place into dst, and dst must have size
-// m×m if svd.Kind() == SVDFull, size m×min(m,n) if svd.Kind() == SVDThin, and
-// UTo panics otherwise. If dst is nil, a new matrix of the appropriate size is
-// allocated and returned.
+// m×m if the full U was computed, size m×min(m,n) if the thin U was computed,
+// and UTo panics otherwise. If dst is nil, a new matrix of the appropriate size
+// is allocated and returned.
 func (svd *SVD) UTo(dst *Dense) *Dense {
+	if !svd.succFact() {
+		panic(badFact)
+	}
 	kind := svd.kind
-	if kind != SVDFull && kind != SVDThin {
-		panic("mat: improper SVD kind")
+	if kind&SVDThinU == 0 && kind&SVDFullU == 0 {
+		panic("svd: u not computed during factorization")
 	}
 	r := svd.u.Rows
 	c := svd.u.Cols
@@ -178,13 +219,16 @@ func (svd *SVD) UTo(dst *Dense) *Dense {
 // values as returned from SVD.Values.
 //
 // If dst is not nil, V is stored in-place into dst, and dst must have size
-// n×n if svd.Kind() == SVDFull, size n×min(m,n) if svd.Kind() == SVDThin, and
-// VTo panics otherwise. If dst is nil, a new matrix of the appropriate size is
-// allocated and returned.
+// n×n if the full V was computed, size n×min(m,n) if the thin V was computed,
+// and VTo panics otherwise. If dst is nil, a new matrix of the appropriate size
+// is allocated and returned.
 func (svd *SVD) VTo(dst *Dense) *Dense {
+	if !svd.succFact() {
+		panic(badFact)
+	}
 	kind := svd.kind
-	if kind != SVDFull && kind != SVDThin {
-		panic("mat: improper SVD kind")
+	if kind&SVDThinU == 0 && kind&SVDFullV == 0 {
+		panic("svd: v not computed during factorization")
 	}
 	r := svd.vt.Rows
 	c := svd.vt.Cols