| // Copyright ©2015 The gonum Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package gonum |
| |
| import "gonum.org/v1/gonum/blas" |
| |
| // Dgebd2 reduces an m×n matrix A to upper or lower bidiagonal form by an orthogonal |
| // transformation. |
| // Q^T * A * P = B |
| // if m >= n, B is upper diagonal, otherwise B is lower bidiagonal. |
| // d is the diagonal, len = min(m,n) |
| // e is the off-diagonal len = min(m,n)-1 |
| // |
| // Dgebd2 is an internal routine. It is exported for testing purposes. |
| func (impl Implementation) Dgebd2(m, n int, a []float64, lda int, d, e, tauQ, tauP, work []float64) { |
| checkMatrix(m, n, a, lda) |
| if len(d) < min(m, n) { |
| panic(badD) |
| } |
| if len(e) < min(m, n)-1 { |
| panic(badE) |
| } |
| if len(tauQ) < min(m, n) { |
| panic(badTauQ) |
| } |
| if len(tauP) < min(m, n) { |
| panic(badTauP) |
| } |
| if len(work) < max(m, n) { |
| panic(badWork) |
| } |
| if m >= n { |
| for i := 0; i < n; i++ { |
| a[i*lda+i], tauQ[i] = impl.Dlarfg(m-i, a[i*lda+i], a[min(i+1, m-1)*lda+i:], lda) |
| d[i] = a[i*lda+i] |
| a[i*lda+i] = 1 |
| // Apply H_i to A[i:m, i+1:n] from the left. |
| if i < n-1 { |
| impl.Dlarf(blas.Left, m-i, n-i-1, a[i*lda+i:], lda, tauQ[i], a[i*lda+i+1:], lda, work) |
| } |
| a[i*lda+i] = d[i] |
| if i < n-1 { |
| 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) |
| e[i] = a[i*lda+i+1] |
| a[i*lda+i+1] = 1 |
| 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) |
| a[i*lda+i+1] = e[i] |
| } else { |
| tauP[i] = 0 |
| } |
| } |
| return |
| } |
| for i := 0; i < m; i++ { |
| a[i*lda+i], tauP[i] = impl.Dlarfg(n-i, a[i*lda+i], a[i*lda+min(i+1, n-1):], 1) |
| d[i] = a[i*lda+i] |
| a[i*lda+i] = 1 |
| if i < m-1 { |
| impl.Dlarf(blas.Right, m-i-1, n-i, a[i*lda+i:], 1, tauP[i], a[(i+1)*lda+i:], lda, work) |
| } |
| a[i*lda+i] = d[i] |
| if i < m-1 { |
| 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) |
| e[i] = a[(i+1)*lda+i] |
| a[(i+1)*lda+i] = 1 |
| 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) |
| a[(i+1)*lda+i] = e[i] |
| } else { |
| tauQ[i] = 0 |
| } |
| } |
| } |