1 // Copyright ©2015 The Gonum Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
7 import "gonum.org/v1/gonum/blas"
9 // Dgebd2 reduces an m×n matrix A to upper or lower bidiagonal form by an orthogonal
12 // if m >= n, B is upper diagonal, otherwise B is lower bidiagonal.
13 // d is the diagonal, len = min(m,n)
14 // e is the off-diagonal len = min(m,n)-1
16 // Dgebd2 is an internal routine. It is exported for testing purposes.
17 func (impl Implementation) Dgebd2(m, n int, a []float64, lda int, d, e, tauQ, tauP, work []float64) {
18 checkMatrix(m, n, a, lda)
19 if len(d) < min(m, n) {
22 if len(e) < min(m, n)-1 {
25 if len(tauQ) < min(m, n) {
28 if len(tauP) < min(m, n) {
31 if len(work) < max(m, n) {
35 for i := 0; i < n; i++ {
36 a[i*lda+i], tauQ[i] = impl.Dlarfg(m-i, a[i*lda+i], a[min(i+1, m-1)*lda+i:], lda)
39 // Apply H_i to A[i:m, i+1:n] from the left.
41 impl.Dlarf(blas.Left, m-i, n-i-1, a[i*lda+i:], lda, tauQ[i], a[i*lda+i+1:], lda, work)
45 a[i*lda+i+1], tauP[i] = impl.Dlarfg(n-i-1, a[i*lda+i+1], a[i*lda+min(i+2, n-1):], 1)
48 impl.Dlarf(blas.Right, m-i-1, n-i-1, a[i*lda+i+1:], 1, tauP[i], a[(i+1)*lda+i+1:], lda, work)
56 for i := 0; i < m; i++ {
57 a[i*lda+i], tauP[i] = impl.Dlarfg(n-i, a[i*lda+i], a[i*lda+min(i+1, n-1):], 1)
61 impl.Dlarf(blas.Right, m-i-1, n-i, a[i*lda+i:], 1, tauP[i], a[(i+1)*lda+i:], lda, work)
65 a[(i+1)*lda+i], tauQ[i] = impl.Dlarfg(m-i-1, a[(i+1)*lda+i], a[min(i+2, m-1)*lda+i:], lda)
68 impl.Dlarf(blas.Left, m-i-1, n-i-1, a[(i+1)*lda+i:], lda, tauQ[i], a[(i+1)*lda+i+1:], lda, work)