LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
Loading...
Searching...
No Matches
slasd0.f
Go to the documentation of this file.
1*> \brief \b SLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and off-diagonal e. Used by sbdsdc.
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8*> \htmlonly
9*> Download SLASD0 + dependencies
10*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slasd0.f">
11*> [TGZ]</a>
12*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slasd0.f">
13*> [ZIP]</a>
14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slasd0.f">
15*> [TXT]</a>
16*> \endhtmlonly
17*
18* Definition:
19* ===========
20*
21* SUBROUTINE SLASD0( N, SQRE, D, E, U, LDU, VT, LDVT, SMLSIZ, IWORK,
22* WORK, INFO )
23*
24* .. Scalar Arguments ..
25* INTEGER INFO, LDU, LDVT, N, SMLSIZ, SQRE
26* ..
27* .. Array Arguments ..
28* INTEGER IWORK( * )
29* REAL D( * ), E( * ), U( LDU, * ), VT( LDVT, * ),
30* $ WORK( * )
31* ..
32*
33*
34*> \par Purpose:
35* =============
36*>
37*> \verbatim
38*>
39*> Using a divide and conquer approach, SLASD0 computes the singular
40*> value decomposition (SVD) of a real upper bidiagonal N-by-M
41*> matrix B with diagonal D and offdiagonal E, where M = N + SQRE.
42*> The algorithm computes orthogonal matrices U and VT such that
43*> B = U * S * VT. The singular values S are overwritten on D.
44*>
45*> A related subroutine, SLASDA, computes only the singular values,
46*> and optionally, the singular vectors in compact form.
47*> \endverbatim
48*
49* Arguments:
50* ==========
51*
52*> \param[in] N
53*> \verbatim
54*> N is INTEGER
55*> On entry, the row dimension of the upper bidiagonal matrix.
56*> This is also the dimension of the main diagonal array D.
57*> \endverbatim
58*>
59*> \param[in] SQRE
60*> \verbatim
61*> SQRE is INTEGER
62*> Specifies the column dimension of the bidiagonal matrix.
63*> = 0: The bidiagonal matrix has column dimension M = N;
64*> = 1: The bidiagonal matrix has column dimension M = N+1;
65*> \endverbatim
66*>
67*> \param[in,out] D
68*> \verbatim
69*> D is REAL array, dimension (N)
70*> On entry D contains the main diagonal of the bidiagonal
71*> matrix.
72*> On exit D, if INFO = 0, contains its singular values.
73*> \endverbatim
74*>
75*> \param[in,out] E
76*> \verbatim
77*> E is REAL array, dimension (M-1)
78*> Contains the subdiagonal entries of the bidiagonal matrix.
79*> On exit, E has been destroyed.
80*> \endverbatim
81*>
82*> \param[out] U
83*> \verbatim
84*> U is REAL array, dimension (LDU, N)
85*> On exit, U contains the left singular vectors.
86*> \endverbatim
87*>
88*> \param[in] LDU
89*> \verbatim
90*> LDU is INTEGER
91*> On entry, leading dimension of U.
92*> \endverbatim
93*>
94*> \param[out] VT
95*> \verbatim
96*> VT is REAL array, dimension (LDVT, M)
97*> On exit, VT**T contains the right singular vectors.
98*> \endverbatim
99*>
100*> \param[in] LDVT
101*> \verbatim
102*> LDVT is INTEGER
103*> On entry, leading dimension of VT.
104*> \endverbatim
105*>
106*> \param[in] SMLSIZ
107*> \verbatim
108*> SMLSIZ is INTEGER
109*> On entry, maximum size of the subproblems at the
110*> bottom of the computation tree.
111*> \endverbatim
112*>
113*> \param[out] IWORK
114*> \verbatim
115*> IWORK is INTEGER array, dimension (8*N)
116*> \endverbatim
117*>
118*> \param[out] WORK
119*> \verbatim
120*> WORK is REAL array, dimension (3*M**2+2*M)
121*> \endverbatim
122*>
123*> \param[out] INFO
124*> \verbatim
125*> INFO is INTEGER
126*> = 0: successful exit.
127*> < 0: if INFO = -i, the i-th argument had an illegal value.
128*> > 0: if INFO = 1, a singular value did not converge
129*> \endverbatim
130*
131* Authors:
132* ========
133*
134*> \author Univ. of Tennessee
135*> \author Univ. of California Berkeley
136*> \author Univ. of Colorado Denver
137*> \author NAG Ltd.
138*
139*> \ingroup OTHERauxiliary
140*
141*> \par Contributors:
142* ==================
143*>
144*> Ming Gu and Huan Ren, Computer Science Division, University of
145*> California at Berkeley, USA
146*>
147* =====================================================================
148 SUBROUTINE slasd0( N, SQRE, D, E, U, LDU, VT, LDVT, SMLSIZ, IWORK,
149 $ WORK, INFO )
150*
151* -- LAPACK auxiliary routine --
152* -- LAPACK is a software package provided by Univ. of Tennessee, --
153* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
154*
155* .. Scalar Arguments ..
156 INTEGER INFO, LDU, LDVT, N, SMLSIZ, SQRE
157* ..
158* .. Array Arguments ..
159 INTEGER IWORK( * )
160 REAL D( * ), E( * ), U( LDU, * ), VT( LDVT, * ),
161 $ work( * )
162* ..
163*
164* =====================================================================
165*
166* .. Local Scalars ..
167 INTEGER I, I1, IC, IDXQ, IDXQC, IM1, INODE, ITEMP, IWK,
168 $ j, lf, ll, lvl, m, ncc, nd, ndb1, ndiml, ndimr,
169 $ nl, nlf, nlp1, nlvl, nr, nrf, nrp1, sqrei
170 REAL ALPHA, BETA
171* ..
172* .. External Subroutines ..
173 EXTERNAL slasd1, slasdq, slasdt, xerbla
174* ..
175* .. Executable Statements ..
176*
177* Test the input parameters.
178*
179 info = 0
180*
181 IF( n.LT.0 ) THEN
182 info = -1
183 ELSE IF( ( sqre.LT.0 ) .OR. ( sqre.GT.1 ) ) THEN
184 info = -2
185 END IF
186*
187 m = n + sqre
188*
189 IF( ldu.LT.n ) THEN
190 info = -6
191 ELSE IF( ldvt.LT.m ) THEN
192 info = -8
193 ELSE IF( smlsiz.LT.3 ) THEN
194 info = -9
195 END IF
196 IF( info.NE.0 ) THEN
197 CALL xerbla( 'SLASD0', -info )
198 RETURN
199 END IF
200*
201* If the input matrix is too small, call SLASDQ to find the SVD.
202*
203 IF( n.LE.smlsiz ) THEN
204 CALL slasdq( 'U', sqre, n, m, n, 0, d, e, vt, ldvt, u, ldu, u,
205 $ ldu, work, info )
206 RETURN
207 END IF
208*
209* Set up the computation tree.
210*
211 inode = 1
212 ndiml = inode + n
213 ndimr = ndiml + n
214 idxq = ndimr + n
215 iwk = idxq + n
216 CALL slasdt( n, nlvl, nd, iwork( inode ), iwork( ndiml ),
217 $ iwork( ndimr ), smlsiz )
218*
219* For the nodes on bottom level of the tree, solve
220* their subproblems by SLASDQ.
221*
222 ndb1 = ( nd+1 ) / 2
223 ncc = 0
224 DO 30 i = ndb1, nd
225*
226* IC : center row of each node
227* NL : number of rows of left subproblem
228* NR : number of rows of right subproblem
229* NLF: starting row of the left subproblem
230* NRF: starting row of the right subproblem
231*
232 i1 = i - 1
233 ic = iwork( inode+i1 )
234 nl = iwork( ndiml+i1 )
235 nlp1 = nl + 1
236 nr = iwork( ndimr+i1 )
237 nrp1 = nr + 1
238 nlf = ic - nl
239 nrf = ic + 1
240 sqrei = 1
241 CALL slasdq( 'U', sqrei, nl, nlp1, nl, ncc, d( nlf ), e( nlf ),
242 $ vt( nlf, nlf ), ldvt, u( nlf, nlf ), ldu,
243 $ u( nlf, nlf ), ldu, work, info )
244 IF( info.NE.0 ) THEN
245 RETURN
246 END IF
247 itemp = idxq + nlf - 2
248 DO 10 j = 1, nl
249 iwork( itemp+j ) = j
250 10 CONTINUE
251 IF( i.EQ.nd ) THEN
252 sqrei = sqre
253 ELSE
254 sqrei = 1
255 END IF
256 nrp1 = nr + sqrei
257 CALL slasdq( 'U', sqrei, nr, nrp1, nr, ncc, d( nrf ), e( nrf ),
258 $ vt( nrf, nrf ), ldvt, u( nrf, nrf ), ldu,
259 $ u( nrf, nrf ), ldu, work, info )
260 IF( info.NE.0 ) THEN
261 RETURN
262 END IF
263 itemp = idxq + ic
264 DO 20 j = 1, nr
265 iwork( itemp+j-1 ) = j
266 20 CONTINUE
267 30 CONTINUE
268*
269* Now conquer each subproblem bottom-up.
270*
271 DO 50 lvl = nlvl, 1, -1
272*
273* Find the first node LF and last node LL on the
274* current level LVL.
275*
276 IF( lvl.EQ.1 ) THEN
277 lf = 1
278 ll = 1
279 ELSE
280 lf = 2**( lvl-1 )
281 ll = 2*lf - 1
282 END IF
283 DO 40 i = lf, ll
284 im1 = i - 1
285 ic = iwork( inode+im1 )
286 nl = iwork( ndiml+im1 )
287 nr = iwork( ndimr+im1 )
288 nlf = ic - nl
289 IF( ( sqre.EQ.0 ) .AND. ( i.EQ.ll ) ) THEN
290 sqrei = sqre
291 ELSE
292 sqrei = 1
293 END IF
294 idxqc = idxq + nlf - 1
295 alpha = d( ic )
296 beta = e( ic )
297 CALL slasd1( nl, nr, sqrei, d( nlf ), alpha, beta,
298 $ u( nlf, nlf ), ldu, vt( nlf, nlf ), ldvt,
299 $ iwork( idxqc ), iwork( iwk ), work, info )
300*
301* Report the possible convergence failure.
302*
303 IF( info.NE.0 ) THEN
304 RETURN
305 END IF
306 40 CONTINUE
307 50 CONTINUE
308*
309 RETURN
310*
311* End of SLASD0
312*
313 END
subroutine slasd0(N, SQRE, D, E, U, LDU, VT, LDVT, SMLSIZ, IWORK, WORK, INFO)
SLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and of...
Definition: slasd0.f:150
subroutine slasd1(NL, NR, SQRE, D, ALPHA, BETA, U, LDU, VT, LDVT, IDXQ, IWORK, WORK, INFO)
SLASD1 computes the SVD of an upper bidiagonal matrix B of the specified size. Used by sbdsdc.
Definition: slasd1.f:204
subroutine slasdq(UPLO, SQRE, N, NCVT, NRU, NCC, D, E, VT, LDVT, U, LDU, C, LDC, WORK, INFO)
SLASDQ computes the SVD of a real bidiagonal matrix with diagonal d and off-diagonal e....
Definition: slasdq.f:211
subroutine slasdt(N, LVL, ND, INODE, NDIML, NDIMR, MSUB)
SLASDT creates a tree of subproblems for bidiagonal divide and conquer. Used by sbdsdc.
Definition: slasdt.f:105
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60