-// 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"
- "gonum.org/v1/gonum/blas/blas64"
-)
-
-// Dorg2r generates an m×n matrix Q with orthonormal columns defined by the
-// product of elementary reflectors as computed by Dgeqrf.
-// Q = H_0 * H_1 * ... * H_{k-1}
-// len(tau) >= k, 0 <= k <= n, 0 <= n <= m, len(work) >= n.
-// Dorg2r will panic if these conditions are not met.
-//
-// Dorg2r is an internal routine. It is exported for testing purposes.
-func (impl Implementation) Dorg2r(m, n, k int, a []float64, lda int, tau []float64, work []float64) {
- checkMatrix(m, n, a, lda)
- if len(tau) < k {
- panic(badTau)
- }
- if len(work) < n {
- panic(badWork)
- }
- if k > n {
- panic(kGTN)
- }
- if n > m {
- panic(mLTN)
- }
- if len(work) < n {
- panic(badWork)
- }
- if n == 0 {
- return
- }
- bi := blas64.Implementation()
- // Initialize columns k+1:n to columns of the unit matrix.
- for l := 0; l < m; l++ {
- for j := k; j < n; j++ {
- a[l*lda+j] = 0
- }
- }
- for j := k; j < n; j++ {
- a[j*lda+j] = 1
- }
- for i := k - 1; i >= 0; i-- {
- for i := range work {
- work[i] = 0
- }
- if i < n-1 {
- a[i*lda+i] = 1
- impl.Dlarf(blas.Left, m-i, n-i-1, a[i*lda+i:], lda, tau[i], a[i*lda+i+1:], lda, work)
- }
- if i < m-1 {
- bi.Dscal(m-i-1, -tau[i], a[(i+1)*lda+i:], lda)
- }
- a[i*lda+i] = 1 - tau[i]
- for l := 0; l < i; l++ {
- a[l*lda+i] = 0
- }
- }
-}