Add dgetrf and tests

removed unnecessary requirement

Implement Dlaswp in both directions

Responded to PR comments

cgo/lapack.go

@@ -13,6 +13,7 @@ import (
 
 // Copied from lapack/native. Keep in sync.
 const (
+	absIncNotOne  = "lapack: increment not one or negative one"
 	badDirect     = "lapack: bad direct"
 	badIpiv       = "lapack: insufficient permutation length"
 	badLdA        = "lapack: index of a out of range"
@@ -76,7 +77,7 @@ func (impl Implementation) Dpotrf(ul blas.Uplo, n int, a []float64, lda int) (ok
 	return clapack.Dpotrf(ul, n, a, lda)
 }
 
-// Dgetf2 computes the LU decomposition of the m×n matrix a.
+// Dgetf2 computes the LU decomposition of the m×n matrix A.
 // The LU decomposition is a factorization of a into
 //  A = P * L * U
 // where P is a permutation matrix, L is a unit lower triangular matrix, and
@@ -85,9 +86,9 @@ func (impl Implementation) Dpotrf(ul blas.Uplo, n int, a []float64, lda int) (ok
 //
 // ipiv is a permutation vector. It indicates that row i of the matrix was
 // changed with ipiv[i]. ipiv must have length at least min(m,n), and will panic
-// otherwise.
+// otherwise. ipiv is zero-indexed.
 //
-// Dgetf2 returns whether the matrix a is singular. The LU decomposition will
+// Dgetf2 returns whether the matrix A is singular. The LU decomposition will
 // be computed regardless of the singularity of A, but division by zero
 // will occur if the false is returned and the result is used to solve a
 // system of equations.
@@ -100,7 +101,38 @@ func (Implementation) Dgetf2(m, n int, a []float64, lda int, ipiv []int) (ok boo
 	ipiv32 := make([]int32, len(ipiv))
 	ok = clapack.Dgetf2(m, n, a, lda, ipiv32)
 	for i, v := range ipiv32 {
-		ipiv[i] = int(v) - 1 // OpenBLAS returns one indexed.
+		ipiv[i] = int(v) - 1 // Transform to zero-indexed.
+	}
+	return ok
+}
+
+// Dgetrf computes the LU decomposition of the m×n matrix A.
+// The LU decomposition is a factorization of a into
+//  A = P * L * U
+// where P is a permutation matrix, L is a unit lower triangular matrix, and
+// U is a (usually) non-unit upper triangular matrix. On exit, L and U are stored
+// in place into a.
+//
+// ipiv is a permutation vector. It indicates that row i of the matrix was
+// changed with ipiv[i]. ipiv must have length at least min(m,n), and will panic
+// otherwise. ipiv is zero-indexed.
+//
+// Dgetrf is the blocked version of the algorithm.
+//
+// Dgetrf returns whether the matrix A is singular. The LU decomposition will
+// be computed regardless of the singularity of A, but division by zero
+// will occur if the false is returned and the result is used to solve a
+// system of equations.
+func (impl Implementation) Dgetrf(m, n int, a []float64, lda int, ipiv []int) (ok bool) {
+	mn := min(m, n)
+	checkMatrix(m, n, a, lda)
+	if len(ipiv) < mn {
+		panic(badIpiv)
+	}
+	ipiv32 := make([]int32, len(ipiv))
+	ok = clapack.Dgetrf(m, n, a, lda, ipiv32)
+	for i, v := range ipiv32 {
+		ipiv[i] = int(v) - 1 // Transform to zero-indexed.
 	}
 	return ok
 }

cgo/lapack_test.go

@@ -19,3 +19,7 @@ func TestDpotrf(t *testing.T) {
 func TestDgetf2(t *testing.T) {
 	testlapack.Dgetf2Test(t, impl)
 }
+
+func TestDgetrf(t *testing.T) {
+	testlapack.DgetrfTest(t, impl)
+}

native/dgeqrf.go

@@ -9,7 +9,7 @@ import (
 	"github.com/gonum/lapack"
 )
 
-// Dgeqrf computes the QR factorization of the m×n matrix a using a blocked
+// Dgeqrf computes the QR factorization of the m×n matrix A using a blocked
 // algorithm. Please see the documentation for Dgeqr2 for a description of the
 // parameters at entry and exit.
 //
@@ -21,9 +21,6 @@ import (
 //
 // tau must be at least len min(m,n), and this function will panic otherwise.
 func (impl Implementation) Dgeqrf(m, n int, a []float64, lda int, tau, work []float64, lwork int) {
-	// TODO(btracey): This algorithm is oriented for column-major storage.
-	// Consider modifying the algorithm to better suit row-major storage.
-
 	// nb is the optimal blocksize, i.e. the number of columns transformed at a time.
 	nb := impl.Ilaenv(1, "DGEQRF", " ", m, n, -1, -1)
 	lworkopt := n * max(nb, 1)

native/dgetf2.go

@@ -6,7 +6,7 @@ import (
 	"github.com/gonum/blas/blas64"
 )
 
-// Dgetf2 computes the LU decomposition of the m×n matrix a.
+// Dgetf2 computes the LU decomposition of the m×n matrix A.
 // The LU decomposition is a factorization of a into
 //  A = P * L * U
 // where P is a permutation matrix, L is a unit lower triangular matrix, and
@@ -15,9 +15,9 @@ import (
 //
 // ipiv is a permutation vector. It indicates that row i of the matrix was
 // changed with ipiv[i]. ipiv must have length at least min(m,n), and will panic
-// otherwise.
+// otherwise. ipiv is zero-indexed.
 //
-// Dgetf2 returns whether the matrix a is singular. The LU decomposition will
+// Dgetf2 returns whether the matrix A is singular. The LU decomposition will
 // be computed regardless of the singularity of A, but division by zero
 // will occur if the false is returned and the result is used to solve a
 // system of equations.

native/dgetrf.go

@@ -0,0 +1,66 @@
+package native
+
+import (
+	"github.com/gonum/blas"
+	"github.com/gonum/blas/blas64"
+)
+
+// Dgetrf computes the LU decomposition of the m×n matrix a.
+// The LU decomposition is a factorization of a into
+//  A = P * L * U
+// where P is a permutation matrix, L is a unit lower triangular matrix, and
+// U is a (usually) non-unit upper triangular matrix. On exit, L and U are stored
+// in place into a.
+//
+// ipiv is a permutation vector. It indicates that row i of the matrix was
+// changed with ipiv[i]. ipiv must have length at least min(m,n), and will panic
+// otherwise. ipiv is zero-indexed.
+//
+// Dgetrf is the blocked version of the algorithm.
+//
+// Dgetrf returns whether the matrix A is singular. The LU decomposition will
+// be computed regardless of the singularity of A, but division by zero
+// will occur if the false is returned and the result is used to solve a
+// system of equations.
+func (impl Implementation) Dgetrf(m, n int, a []float64, lda int, ipiv []int) (ok bool) {
+	mn := min(m, n)
+	checkMatrix(m, n, a, lda)
+	if len(ipiv) < mn {
+		panic(badIpiv)
+	}
+	if m == 0 || n == 0 {
+		return
+	}
+	bi := blas64.Implementation()
+	nb := impl.Ilaenv(1, "DGETRF", " ", m, n, -1, -1)
+	if nb <= 1 || nb >= min(m, n) {
+		// Use the unblocked algorithm.
+		return impl.Dgetf2(m, n, a, lda, ipiv)
+	}
+	ok = true
+	for j := 0; j < mn; j += nb {
+		jb := min(mn-j, nb)
+		blockOk := impl.Dgetf2(m-j, jb, a[j*lda+j:], lda, ipiv[j:])
+		if !blockOk {
+			ok = false
+		}
+		for i := j; i <= min(m-1, j+jb-1); i++ {
+			ipiv[i] = j + ipiv[i]
+		}
+		impl.Dlaswp(j, a, lda, j, j+jb-1, ipiv, 1)
+		if j+jb < n {
+			impl.Dlaswp(n-j-jb, a[j+jb:], lda, j, j+jb-1, ipiv, 1)
+			bi.Dtrsm(blas.Left, blas.Lower, blas.NoTrans, blas.Unit,
+				jb, n-j-jb, 1,
+				a[j*lda+j:], lda,
+				a[j*lda+j+jb:], lda)
+			if j+jb < m {
+				bi.Dgemm(blas.NoTrans, blas.NoTrans, m-j-jb, n-j-jb, jb, -1,
+					a[(j+jb)*lda+j:], lda,
+					a[j*lda+j+jb:], lda,
+					1, a[(j+jb)*lda+j+jb:], lda)
+			}
+		}
+	}
+	return ok
+}

native/dlaswp.go

@@ -0,0 +1,23 @@
+package native
+
+import "github.com/gonum/blas/blas64"
+
+// Dlaswp swaps the rows k1 to k2 of a according to the indices in ipiv.
+// a is a matrix with n columns and stride lda. incX is the increment for ipiv.
+// k1 and k2 are zero-indexed. If incX is negative, then loops from k2 to k1
+func (impl Implementation) Dlaswp(n int, a []float64, lda, k1, k2 int, ipiv []int, incX int) {
+	if incX != 1 && incX != -1 {
+		panic(absIncNotOne)
+	}
+	bi := blas64.Implementation()
+	if incX == 1 {
+		for k := k1; k <= k2; k++ {
+			bi.Dswap(n, a[k*lda:], 1, a[ipiv[k]*lda:], 1)
+		}
+		return
+	}
+	for k := k2; k >= k1; k-- {
+		bi.Dswap(n, a[k*lda:], 1, a[ipiv[k]*lda:], 1)
+	}
+	return
+}

native/general.go

@@ -17,7 +17,9 @@ type Implementation struct{}
 
 var _ lapack.Float64 = Implementation{}
 
+// This list is duplicated in lapack/cgo. Keep in sync.
 const (
+	absIncNotOne  = "lapack: increment not one or negative one"
 	badDirect     = "lapack: bad direct"
 	badIpiv       = "lapack: insufficient permutation length"
 	badLdA        = "lapack: index of a out of range"

native/lapack_test.go

@@ -36,6 +36,10 @@ func TestDgetf2(t *testing.T) {
 	testlapack.Dgetf2Test(t, impl)
 }
 
+func TestDgetrf(t *testing.T) {
+	testlapack.DgetrfTest(t, impl)
+}
+
 func TestDlange(t *testing.T) {
 	testlapack.DlangeTest(t, impl)
 }

testlapack/dgetf2.go

@@ -40,86 +40,11 @@ func Dgetf2Test(t *testing.T, impl Dgetf2er) {
 
 		mn := min(m, n)
 		ipiv := make([]int, mn)
+		for i := range ipiv {
+			ipiv[i] = rand.Int()
+		}
 		ok := impl.Dgetf2(m, n, a, lda, ipiv)
-		var hasZeroDiagonal bool
-		for i := 0; i < min(m, n); i++ {
-			if a[i*lda+i] == 0 {
-				hasZeroDiagonal = true
-				break
-			}
-		}
-		if hasZeroDiagonal && ok {
-			t.Errorf("Has a zero diagonal but returned ok")
-		}
-		if !hasZeroDiagonal && !ok {
-			t.Errorf("Non-zero diagonal but returned !ok")
-		}
-		// Check that the LU decomposition is correct.
-		l := make([]float64, m*mn)
-		ldl := mn
-		u := make([]float64, mn*n)
-		ldu := n
-		for i := 0; i < m; i++ {
-			for j := 0; j < n; j++ {
-				v := a[i*lda+j]
-				switch {
-				case i == j:
-					l[i*ldl+i] = 1
-					u[i*ldu+i] = v
-				case i > j:
-					l[i*ldl+j] = v
-				case i < j:
-					u[i*ldu+j] = v
-				}
-			}
-		}
-
-		LU := blas64.General{
-			Rows:   m,
-			Cols:   n,
-			Stride: n,
-			Data:   make([]float64, m*n),
-		}
-		U := blas64.General{
-			Rows:   mn,
-			Cols:   n,
-			Stride: ldu,
-			Data:   u,
-		}
-		L := blas64.General{
-			Rows:   m,
-			Cols:   mn,
-			Stride: ldl,
-			Data:   l,
-		}
-		blas64.Gemm(blas.NoTrans, blas.NoTrans, 1, L, U, 0, LU)
-
-		p := make([]float64, m*m)
-		ldp := m
-		for i := 0; i < m; i++ {
-			p[i*ldp+i] = 1
-		}
-		for i := len(ipiv) - 1; i >= 0; i-- {
-			v := ipiv[i]
-			blas64.Swap(m, blas64.Vector{1, p[i*ldp:]}, blas64.Vector{1, p[v*ldp:]})
-		}
-		P := blas64.General{
-			Rows:   m,
-			Cols:   m,
-			Stride: m,
-			Data:   p,
-		}
-		aComp := blas64.General{
-			Rows:   m,
-			Cols:   n,
-			Stride: lda,
-			Data:   make([]float64, m*lda),
-		}
-		copy(aComp.Data, a)
-		blas64.Gemm(blas.NoTrans, blas.NoTrans, 1, P, LU, 0, aComp)
-		if !floats.EqualApprox(aComp.Data, aCopy, 1e-14) {
-			t.Errorf("Answer mismatch.\nWant\n %v,\nGot %v.", aCopy, aComp.Data)
-		}
+		checkPLU(t, ok, m, n, lda, ipiv, a, aCopy, 1e-14, true)
 	}
 
 	// Test with singular matrices (random matrices are almost surely non-singular).
@@ -173,3 +98,93 @@ func Dgetf2Test(t *testing.T, impl Dgetf2er) {
 		}
 	}
 }
+
+// checkPLU checks that the PLU factorization contained in factorize matches
+// the original matrix contained in original.
+func checkPLU(t *testing.T, ok bool, m, n, lda int, ipiv []int, factorized, original []float64, tol float64, print bool) {
+	var hasZeroDiagonal bool
+	for i := 0; i < min(m, n); i++ {
+		if factorized[i*lda+i] == 0 {
+			hasZeroDiagonal = true
+			break
+		}
+	}
+	if hasZeroDiagonal && ok {
+		t.Errorf("Has a zero diagonal but returned ok")
+	}
+	if !hasZeroDiagonal && !ok {
+		t.Errorf("Non-zero diagonal but returned !ok")
+	}
+
+	// Check that the LU decomposition is correct.
+	mn := min(m, n)
+	l := make([]float64, m*mn)
+	ldl := mn
+	u := make([]float64, mn*n)
+	ldu := n
+	for i := 0; i < m; i++ {
+		for j := 0; j < n; j++ {
+			v := factorized[i*lda+j]
+			switch {
+			case i == j:
+				l[i*ldl+i] = 1
+				u[i*ldu+i] = v
+			case i > j:
+				l[i*ldl+j] = v
+			case i < j:
+				u[i*ldu+j] = v
+			}
+		}
+	}
+
+	LU := blas64.General{
+		Rows:   m,
+		Cols:   n,
+		Stride: n,
+		Data:   make([]float64, m*n),
+	}
+	U := blas64.General{
+		Rows:   mn,
+		Cols:   n,
+		Stride: ldu,
+		Data:   u,
+	}
+	L := blas64.General{
+		Rows:   m,
+		Cols:   mn,
+		Stride: ldl,
+		Data:   l,
+	}
+	blas64.Gemm(blas.NoTrans, blas.NoTrans, 1, L, U, 0, LU)
+
+	p := make([]float64, m*m)
+	ldp := m
+	for i := 0; i < m; i++ {
+		p[i*ldp+i] = 1
+	}
+	for i := len(ipiv) - 1; i >= 0; i-- {
+		v := ipiv[i]
+		blas64.Swap(m, blas64.Vector{1, p[i*ldp:]}, blas64.Vector{1, p[v*ldp:]})
+	}
+	P := blas64.General{
+		Rows:   m,
+		Cols:   m,
+		Stride: m,
+		Data:   p,
+	}
+	aComp := blas64.General{
+		Rows:   m,
+		Cols:   n,
+		Stride: lda,
+		Data:   make([]float64, m*lda),
+	}
+	copy(aComp.Data, factorized)
+	blas64.Gemm(blas.NoTrans, blas.NoTrans, 1, P, LU, 0, aComp)
+	if !floats.EqualApprox(aComp.Data, original, tol) {
+		if print {
+			t.Errorf("PLU multiplication does not match original matrix.\nWant: %v\nGot: %v", original, aComp.Data)
+			return
+		}
+		t.Errorf("PLU multiplication does not match original matrix.")
+	}
+}

testlapack/dgetrf.go

@@ -0,0 +1,60 @@
+package testlapack
+
+import (
+	"math/rand"
+	"testing"
+)
+
+type Dgetrfer interface {
+	Dgetrf(m, n int, a []float64, lda int, ipiv []int) bool
+}
+
+func DgetrfTest(t *testing.T, impl Dgetrfer) {
+	for _, test := range []struct {
+		m, n, lda int
+	}{
+		{10, 5, 0},
+		{5, 10, 0},
+		{10, 10, 0},
+		{300, 5, 0},
+		{3, 500, 0},
+		{4, 5, 0},
+		{300, 200, 0},
+		{204, 300, 0},
+		{1, 3000, 0},
+		{3000, 1, 0},
+		{10, 5, 20},
+		{5, 10, 20},
+		{10, 10, 20},
+		{300, 5, 400},
+		{3, 500, 600},
+		{200, 200, 300},
+		{300, 200, 300},
+		{204, 300, 400},
+		{1, 3000, 4000},
+		{3000, 1, 4000},
+	} {
+		m := test.m
+		n := test.n
+		lda := test.lda
+		if lda == 0 {
+			lda = n
+		}
+		a := make([]float64, m*lda)
+		for i := range a {
+			a[i] = rand.Float64()
+		}
+		mn := min(m, n)
+		ipiv := make([]int, mn)
+		for i := range ipiv {
+			ipiv[i] = rand.Int()
+		}
+
+		// Cannot compare the outputs of Dgetrf and Dgetf2 because the pivoting may
+		// happen differently. Instead check that the LPQ factorization is correct.
+		aCopy := make([]float64, len(a))
+		copy(aCopy, a)
+		ok := impl.Dgetrf(m, n, a, lda, ipiv)
+		checkPLU(t, ok, m, n, lda, ipiv, a, aCopy, 1e-10, false)
+	}
+}