LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ sormql()

subroutine sormql ( character  SIDE,
character  TRANS,
integer  M,
integer  N,
integer  K,
real, dimension( lda, * )  A,
integer  LDA,
real, dimension( * )  TAU,
real, dimension( ldc, * )  C,
integer  LDC,
real, dimension( * )  WORK,
integer  LWORK,
integer  INFO 
)

SORMQL

Download SORMQL + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 SORMQL overwrites the general real M-by-N matrix C with

                 SIDE = 'L'     SIDE = 'R'
 TRANS = 'N':      Q * C          C * Q
 TRANS = 'T':      Q**T * C       C * Q**T

 where Q is a real orthogonal matrix defined as the product of k
 elementary reflectors

       Q = H(k) . . . H(2) H(1)

 as returned by SGEQLF. Q is of order M if SIDE = 'L' and of order N
 if SIDE = 'R'.
Parameters
[in]SIDE
          SIDE is CHARACTER*1
          = 'L': apply Q or Q**T from the Left;
          = 'R': apply Q or Q**T from the Right.
[in]TRANS
          TRANS is CHARACTER*1
          = 'N':  No transpose, apply Q;
          = 'T':  Transpose, apply Q**T.
[in]M
          M is INTEGER
          The number of rows of the matrix C. M >= 0.
[in]N
          N is INTEGER
          The number of columns of the matrix C. N >= 0.
[in]K
          K is INTEGER
          The number of elementary reflectors whose product defines
          the matrix Q.
          If SIDE = 'L', M >= K >= 0;
          if SIDE = 'R', N >= K >= 0.
[in]A
          A is REAL array, dimension (LDA,K)
          The i-th column must contain the vector which defines the
          elementary reflector H(i), for i = 1,2,...,k, as returned by
          SGEQLF in the last k columns of its array argument A.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.
          If SIDE = 'L', LDA >= max(1,M);
          if SIDE = 'R', LDA >= max(1,N).
[in]TAU
          TAU is REAL array, dimension (K)
          TAU(i) must contain the scalar factor of the elementary
          reflector H(i), as returned by SGEQLF.
[in,out]C
          C is REAL array, dimension (LDC,N)
          On entry, the M-by-N matrix C.
          On exit, C is overwritten by Q*C or Q**T*C or C*Q**T or C*Q.
[in]LDC
          LDC is INTEGER
          The leading dimension of the array C. LDC >= max(1,M).
[out]WORK
          WORK is REAL array, dimension (MAX(1,LWORK))
          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
[in]LWORK
          LWORK is INTEGER
          The dimension of the array WORK.
          If SIDE = 'L', LWORK >= max(1,N);
          if SIDE = 'R', LWORK >= max(1,M).
          For good performance, LWORK should generally be larger.

          If LWORK = -1, then a workspace query is assumed; the routine
          only calculates the optimal size of the WORK array, returns
          this value as the first entry of the WORK array, and no error
          message related to LWORK is issued by XERBLA.
[out]INFO
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 166 of file sormql.f.

168*
169* -- LAPACK computational routine --
170* -- LAPACK is a software package provided by Univ. of Tennessee, --
171* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
172*
173* .. Scalar Arguments ..
174 CHARACTER SIDE, TRANS
175 INTEGER INFO, K, LDA, LDC, LWORK, M, N
176* ..
177* .. Array Arguments ..
178 REAL A( LDA, * ), C( LDC, * ), TAU( * ),
179 $ WORK( * )
180* ..
181*
182* =====================================================================
183*
184* .. Parameters ..
185 INTEGER NBMAX, LDT, TSIZE
186 parameter( nbmax = 64, ldt = nbmax+1,
187 $ tsize = ldt*nbmax )
188* ..
189* .. Local Scalars ..
190 LOGICAL LEFT, LQUERY, NOTRAN
191 INTEGER I, I1, I2, I3, IB, IINFO, IWT, LDWORK, LWKOPT,
192 $ MI, NB, NBMIN, NI, NQ, NW
193* ..
194* .. External Functions ..
195 LOGICAL LSAME
196 INTEGER ILAENV
197 EXTERNAL lsame, ilaenv
198* ..
199* .. External Subroutines ..
200 EXTERNAL slarfb, slarft, sorm2l, xerbla
201* ..
202* .. Intrinsic Functions ..
203 INTRINSIC max, min
204* ..
205* .. Executable Statements ..
206*
207* Test the input arguments
208*
209 info = 0
210 left = lsame( side, 'L' )
211 notran = lsame( trans, 'N' )
212 lquery = ( lwork.EQ.-1 )
213*
214* NQ is the order of Q and NW is the minimum dimension of WORK
215*
216 IF( left ) THEN
217 nq = m
218 nw = max( 1, n )
219 ELSE
220 nq = n
221 nw = max( 1, m )
222 END IF
223 IF( .NOT.left .AND. .NOT.lsame( side, 'R' ) ) THEN
224 info = -1
225 ELSE IF( .NOT.notran .AND. .NOT.lsame( trans, 'T' ) ) THEN
226 info = -2
227 ELSE IF( m.LT.0 ) THEN
228 info = -3
229 ELSE IF( n.LT.0 ) THEN
230 info = -4
231 ELSE IF( k.LT.0 .OR. k.GT.nq ) THEN
232 info = -5
233 ELSE IF( lda.LT.max( 1, nq ) ) THEN
234 info = -7
235 ELSE IF( ldc.LT.max( 1, m ) ) THEN
236 info = -10
237 ELSE IF( lwork.LT.nw .AND. .NOT.lquery ) THEN
238 info = -12
239 END IF
240*
241 IF( info.EQ.0 ) THEN
242*
243* Compute the workspace requirements
244*
245 IF( m.EQ.0 .OR. n.EQ.0 ) THEN
246 lwkopt = 1
247 ELSE
248 nb = min( nbmax, ilaenv( 1, 'SORMQL', side // trans, m, n,
249 $ k, -1 ) )
250 lwkopt = nw*nb + tsize
251 END IF
252 work( 1 ) = lwkopt
253 END IF
254*
255 IF( info.NE.0 ) THEN
256 CALL xerbla( 'SORMQL', -info )
257 RETURN
258 ELSE IF( lquery ) THEN
259 RETURN
260 END IF
261*
262* Quick return if possible
263*
264 IF( m.EQ.0 .OR. n.EQ.0 ) THEN
265 RETURN
266 END IF
267*
268 nbmin = 2
269 ldwork = nw
270 IF( nb.GT.1 .AND. nb.LT.k ) THEN
271 IF( lwork.LT.lwkopt ) THEN
272 nb = (lwork-tsize) / ldwork
273 nbmin = max( 2, ilaenv( 2, 'SORMQL', side // trans, m, n, k,
274 $ -1 ) )
275 END IF
276 END IF
277*
278 IF( nb.LT.nbmin .OR. nb.GE.k ) THEN
279*
280* Use unblocked code
281*
282 CALL sorm2l( side, trans, m, n, k, a, lda, tau, c, ldc, work,
283 $ iinfo )
284 ELSE
285*
286* Use blocked code
287*
288 iwt = 1 + nw*nb
289 IF( ( left .AND. notran ) .OR.
290 $ ( .NOT.left .AND. .NOT.notran ) ) THEN
291 i1 = 1
292 i2 = k
293 i3 = nb
294 ELSE
295 i1 = ( ( k-1 ) / nb )*nb + 1
296 i2 = 1
297 i3 = -nb
298 END IF
299*
300 IF( left ) THEN
301 ni = n
302 ELSE
303 mi = m
304 END IF
305*
306 DO 10 i = i1, i2, i3
307 ib = min( nb, k-i+1 )
308*
309* Form the triangular factor of the block reflector
310* H = H(i+ib-1) . . . H(i+1) H(i)
311*
312 CALL slarft( 'Backward', 'Columnwise', nq-k+i+ib-1, ib,
313 $ a( 1, i ), lda, tau( i ), work( iwt ), ldt )
314 IF( left ) THEN
315*
316* H or H**T is applied to C(1:m-k+i+ib-1,1:n)
317*
318 mi = m - k + i + ib - 1
319 ELSE
320*
321* H or H**T is applied to C(1:m,1:n-k+i+ib-1)
322*
323 ni = n - k + i + ib - 1
324 END IF
325*
326* Apply H or H**T
327*
328 CALL slarfb( side, trans, 'Backward', 'Columnwise', mi, ni,
329 $ ib, a( 1, i ), lda, work( iwt ), ldt, c, ldc,
330 $ work, ldwork )
331 10 CONTINUE
332 END IF
333 work( 1 ) = lwkopt
334 RETURN
335*
336* End of SORMQL
337*
ilaenv
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
ILAENV
Definition: ilaenv.f:162
xerbla
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
lsame
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
slarfb
subroutine slarfb(SIDE, TRANS, DIRECT, STOREV, M, N, K, V, LDV, T, LDT, C, LDC, WORK, LDWORK)
SLARFB applies a block reflector or its transpose to a general rectangular matrix.
Definition: slarfb.f:197
slarft
subroutine slarft(DIRECT, STOREV, N, K, V, LDV, TAU, T, LDT)
SLARFT forms the triangular factor T of a block reflector H = I - vtvH
Definition: slarft.f:163
sorm2l
subroutine sorm2l(SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, INFO)
SORM2L multiplies a general matrix by the orthogonal matrix from a QL factorization determined by sge...
Definition: sorm2l.f:159
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