1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
|
// 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) {
switch {
case m < 0:
panic(mLT0)
case n < 0:
panic(nLT0)
case n > m:
panic(nGTM)
case k < 0:
panic(kLT0)
case k > n:
panic(kGTN)
case lda < max(1, n):
panic(badLdA)
}
if n == 0 {
return
}
switch {
case len(a) < (m-1)*lda+n:
panic(shortA)
case len(tau) != k:
panic(badLenTau)
case len(work) < n:
panic(shortWork)
}
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
}
}
}
|
