1
*> \brief \b ZGEBD2 reduces a general matrix to bidiagonal form using an unblocked algorithm.
3
* =========== DOCUMENTATION ===========
5
* Online html documentation available at
6
* http://www.netlib.org/lapack/explore-html/
9
*> Download ZGEBD2 + dependencies
10
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zgebd2.f">
12
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zgebd2.f">
14
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zgebd2.f">
21
* SUBROUTINE ZGEBD2( M, N, A, LDA, D, E, TAUQ, TAUP, WORK, INFO )
23
* .. Scalar Arguments ..
24
* INTEGER INFO, LDA, M, N
26
* .. Array Arguments ..
27
* DOUBLE PRECISION D( * ), E( * )
28
* COMPLEX*16 A( LDA, * ), TAUP( * ), TAUQ( * ), WORK( * )
37
*> ZGEBD2 reduces a complex general m by n matrix A to upper or lower
38
*> real bidiagonal form B by a unitary transformation: Q**H * A * P = B.
40
*> If m >= n, B is upper bidiagonal; if m < n, B is lower bidiagonal.
49
*> The number of rows in the matrix A. M >= 0.
55
*> The number of columns in the matrix A. N >= 0.
60
*> A is COMPLEX*16 array, dimension (LDA,N)
61
*> On entry, the m by n general matrix to be reduced.
63
*> if m >= n, the diagonal and the first superdiagonal are
64
*> overwritten with the upper bidiagonal matrix B; the
65
*> elements below the diagonal, with the array TAUQ, represent
66
*> the unitary matrix Q as a product of elementary
67
*> reflectors, and the elements above the first superdiagonal,
68
*> with the array TAUP, represent the unitary matrix P as
69
*> a product of elementary reflectors;
70
*> if m < n, the diagonal and the first subdiagonal are
71
*> overwritten with the lower bidiagonal matrix B; the
72
*> elements below the first subdiagonal, with the array TAUQ,
73
*> represent the unitary matrix Q as a product of
74
*> elementary reflectors, and the elements above the diagonal,
75
*> with the array TAUP, represent the unitary matrix P as
76
*> a product of elementary reflectors.
77
*> See Further Details.
83
*> The leading dimension of the array A. LDA >= max(1,M).
88
*> D is DOUBLE PRECISION array, dimension (min(M,N))
89
*> The diagonal elements of the bidiagonal matrix B:
95
*> E is DOUBLE PRECISION array, dimension (min(M,N)-1)
96
*> The off-diagonal elements of the bidiagonal matrix B:
97
*> if m >= n, E(i) = A(i,i+1) for i = 1,2,...,n-1;
98
*> if m < n, E(i) = A(i+1,i) for i = 1,2,...,m-1.
103
*> TAUQ is COMPLEX*16 array dimension (min(M,N))
104
*> The scalar factors of the elementary reflectors which
105
*> represent the unitary matrix Q. See Further Details.
110
*> TAUP is COMPLEX*16 array, dimension (min(M,N))
111
*> The scalar factors of the elementary reflectors which
112
*> represent the unitary matrix P. See Further Details.
117
*> WORK is COMPLEX*16 array, dimension (max(M,N))
123
*> = 0: successful exit
124
*> < 0: if INFO = -i, the i-th argument had an illegal value.
130
*> \author Univ. of Tennessee
131
*> \author Univ. of California Berkeley
132
*> \author Univ. of Colorado Denver
135
*> \date September 2012
137
*> \ingroup complex16GEcomputational
139
*> \par Further Details:
140
* =====================
144
*> The matrices Q and P are represented as products of elementary
149
*> Q = H(1) H(2) . . . H(n) and P = G(1) G(2) . . . G(n-1)
151
*> Each H(i) and G(i) has the form:
153
*> H(i) = I - tauq * v * v**H and G(i) = I - taup * u * u**H
155
*> where tauq and taup are complex scalars, and v and u are complex
156
*> vectors; v(1:i-1) = 0, v(i) = 1, and v(i+1:m) is stored on exit in
157
*> A(i+1:m,i); u(1:i) = 0, u(i+1) = 1, and u(i+2:n) is stored on exit in
158
*> A(i,i+2:n); tauq is stored in TAUQ(i) and taup in TAUP(i).
162
*> Q = H(1) H(2) . . . H(m-1) and P = G(1) G(2) . . . G(m)
164
*> Each H(i) and G(i) has the form:
166
*> H(i) = I - tauq * v * v**H and G(i) = I - taup * u * u**H
168
*> where tauq and taup are complex scalars, v and u are complex vectors;
169
*> v(1:i) = 0, v(i+1) = 1, and v(i+2:m) is stored on exit in A(i+2:m,i);
170
*> u(1:i-1) = 0, u(i) = 1, and u(i+1:n) is stored on exit in A(i,i+1:n);
171
*> tauq is stored in TAUQ(i) and taup in TAUP(i).
173
*> The contents of A on exit are illustrated by the following examples:
175
*> m = 6 and n = 5 (m > n): m = 5 and n = 6 (m < n):
177
*> ( d e u1 u1 u1 ) ( d u1 u1 u1 u1 u1 )
178
*> ( v1 d e u2 u2 ) ( e d u2 u2 u2 u2 )
179
*> ( v1 v2 d e u3 ) ( v1 e d u3 u3 u3 )
180
*> ( v1 v2 v3 d e ) ( v1 v2 e d u4 u4 )
181
*> ( v1 v2 v3 v4 d ) ( v1 v2 v3 e d u5 )
182
*> ( v1 v2 v3 v4 v5 )
184
*> where d and e denote diagonal and off-diagonal elements of B, vi
185
*> denotes an element of the vector defining H(i), and ui an element of
186
*> the vector defining G(i).
189
* =====================================================================
190
SUBROUTINE ZGEBD2( M, N, A, LDA, D, E, TAUQ, TAUP, WORK, INFO )
192
* -- LAPACK computational routine (version 3.4.2) --
193
* -- LAPACK is a software package provided by Univ. of Tennessee, --
194
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
197
* .. Scalar Arguments ..
198
INTEGER INFO, LDA, M, N
200
* .. Array Arguments ..
201
DOUBLE PRECISION D( * ), E( * )
202
COMPLEX*16 A( LDA, * ), TAUP( * ), TAUQ( * ), WORK( * )
205
* =====================================================================
209
PARAMETER ( ZERO = ( 0.0D+0, 0.0D+0 ),
210
$ ONE = ( 1.0D+0, 0.0D+0 ) )
212
* .. Local Scalars ..
216
* .. External Subroutines ..
217
EXTERNAL XERBLA, ZLACGV, ZLARF, ZLARFG
219
* .. Intrinsic Functions ..
220
INTRINSIC DCONJG, MAX, MIN
222
* .. Executable Statements ..
224
* Test the input parameters
229
ELSE IF( N.LT.0 ) THEN
231
ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
235
CALL XERBLA( 'ZGEBD2', -INFO )
241
* Reduce to upper bidiagonal form
245
* Generate elementary reflector H(i) to annihilate A(i+1:m,i)
248
CALL ZLARFG( M-I+1, ALPHA, A( MIN( I+1, M ), I ), 1,
253
* Apply H(i)**H to A(i:m,i+1:n) from the left
256
$ CALL ZLARF( 'Left', M-I+1, N-I, A( I, I ), 1,
257
$ DCONJG( TAUQ( I ) ), A( I, I+1 ), LDA, WORK )
262
* Generate elementary reflector G(i) to annihilate
265
CALL ZLACGV( N-I, A( I, I+1 ), LDA )
267
CALL ZLARFG( N-I, ALPHA, A( I, MIN( I+2, N ) ), LDA,
272
* Apply G(i) to A(i+1:m,i+1:n) from the right
274
CALL ZLARF( 'Right', M-I, N-I, A( I, I+1 ), LDA,
275
$ TAUP( I ), A( I+1, I+1 ), LDA, WORK )
276
CALL ZLACGV( N-I, A( I, I+1 ), LDA )
284
* Reduce to lower bidiagonal form
288
* Generate elementary reflector G(i) to annihilate A(i,i+1:n)
290
CALL ZLACGV( N-I+1, A( I, I ), LDA )
292
CALL ZLARFG( N-I+1, ALPHA, A( I, MIN( I+1, N ) ), LDA,
297
* Apply G(i) to A(i+1:m,i:n) from the right
300
$ CALL ZLARF( 'Right', M-I, N-I+1, A( I, I ), LDA,
301
$ TAUP( I ), A( I+1, I ), LDA, WORK )
302
CALL ZLACGV( N-I+1, A( I, I ), LDA )
307
* Generate elementary reflector H(i) to annihilate
311
CALL ZLARFG( M-I, ALPHA, A( MIN( I+2, M ), I ), 1,
316
* Apply H(i)**H to A(i+1:m,i+1:n) from the left
318
CALL ZLARF( 'Left', M-I, N-I, A( I+1, I ), 1,
319
$ DCONJG( TAUQ( I ) ), A( I+1, I+1 ), LDA,