1 // Copyright ©2016 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 // Dorghr generates an n×n orthogonal matrix Q which is defined as the product
8 // of ihi-ilo elementary reflectors:
9 // Q = H_{ilo} H_{ilo+1} ... H_{ihi-1}.
11 // a and lda represent an n×n matrix that contains the elementary reflectors, as
12 // returned by Dgehrd. On return, a is overwritten by the n×n orthogonal matrix
13 // Q. Q will be equal to the identity matrix except in the submatrix
14 // Q[ilo+1:ihi+1,ilo+1:ihi+1].
16 // ilo and ihi must have the same values as in the previous call of Dgehrd. It
18 // 0 <= ilo <= ihi < n, if n > 0,
19 // ilo = 0, ihi = -1, if n == 0.
21 // tau contains the scalar factors of the elementary reflectors, as returned by
22 // Dgehrd. tau must have length n-1.
24 // work must have length at least max(1,lwork) and lwork must be at least
25 // ihi-ilo. For optimum performance lwork must be at least (ihi-ilo)*nb where nb
26 // is the optimal blocksize. On return, work[0] will contain the optimal value
29 // If lwork == -1, instead of performing Dorghr, only the optimal value of lwork
30 // will be stored into work[0].
32 // If any requirement on input sizes is not met, Dorghr will panic.
34 // Dorghr is an internal routine. It is exported for testing purposes.
35 func (impl Implementation) Dorghr(n, ilo, ihi int, a []float64, lda int, tau, work []float64, lwork int) {
36 checkMatrix(n, n, a, lda)
39 case ilo < 0 || max(1, n) <= ilo:
41 case ihi < min(ilo, n-1) || n <= ihi:
43 case lwork < max(1, nh) && lwork != -1:
45 case len(work) < max(1, lwork):
49 lwkopt := max(1, nh) * impl.Ilaenv(1, "DORGQR", " ", nh, nh, nh, -1)
51 work[0] = float64(lwkopt)
55 // Quick return if possible.
61 // Shift the vectors which define the elementary reflectors one column
63 for i := ilo + 2; i < ihi+1; i++ {
64 copy(a[i*lda+ilo+1:i*lda+i], a[i*lda+ilo:i*lda+i-1])
66 // Set the first ilo+1 and the last n-ihi-1 rows and columns to those of
67 // the identity matrix.
68 for i := 0; i < ilo+1; i++ {
69 for j := 0; j < n; j++ {
74 for i := ilo + 1; i < ihi+1; i++ {
75 for j := 0; j <= ilo; j++ {
78 for j := i; j < n; j++ {
82 for i := ihi + 1; i < n; i++ {
83 for j := 0; j < n; j++ {
89 // Generate Q[ilo+1:ihi+1,ilo+1:ihi+1].
90 impl.Dorgqr(nh, nh, nh, a[(ilo+1)*lda+ilo+1:], lda, tau[ilo:ihi], work, lwork)
92 work[0] = float64(lwkopt)