LAPACK  3.10.1 LAPACK: Linear Algebra PACKage

## ◆ sgelsd()

 subroutine sgelsd ( integer M, integer N, integer NRHS, real, dimension( lda, * ) A, integer LDA, real, dimension( ldb, * ) B, integer LDB, real, dimension( * ) S, real RCOND, integer RANK, real, dimension( * ) WORK, integer LWORK, integer, dimension( * ) IWORK, integer INFO )

SGELSD computes the minimum-norm solution to a linear least squares problem for GE matrices

Purpose:
``` SGELSD computes the minimum-norm solution to a real linear least
squares problem:
minimize 2-norm(| b - A*x |)
using the singular value decomposition (SVD) of A. A is an M-by-N
matrix which may be rank-deficient.

Several right hand side vectors b and solution vectors x can be
handled in a single call; they are stored as the columns of the
M-by-NRHS right hand side matrix B and the N-by-NRHS solution
matrix X.

The problem is solved in three steps:
(1) Reduce the coefficient matrix A to bidiagonal form with
Householder transformations, reducing the original problem
into a "bidiagonal least squares problem" (BLS)
(2) Solve the BLS using a divide and conquer approach.
(3) Apply back all the Householder transformations to solve
the original least squares problem.

The effective rank of A is determined by treating as zero those
singular values which are less than RCOND times the largest singular
value.

The divide and conquer algorithm makes very mild assumptions about
floating point arithmetic. It will work on machines with a guard
digit in add/subtract, or on those binary machines without guard
digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or
Cray-2. It could conceivably fail on hexadecimal or decimal machines
without guard digits, but we know of none.```
Parameters
 [in] M ``` M is INTEGER The number of rows of A. M >= 0.``` [in] N ``` N is INTEGER The number of columns of A. N >= 0.``` [in] NRHS ``` NRHS is INTEGER The number of right hand sides, i.e., the number of columns of the matrices B and X. NRHS >= 0.``` [in,out] A ``` A is REAL array, dimension (LDA,N) On entry, the M-by-N matrix A. On exit, A has been destroyed.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,M).``` [in,out] B ``` B is REAL array, dimension (LDB,NRHS) On entry, the M-by-NRHS right hand side matrix B. On exit, B is overwritten by the N-by-NRHS solution matrix X. If m >= n and RANK = n, the residual sum-of-squares for the solution in the i-th column is given by the sum of squares of elements n+1:m in that column.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1,max(M,N)).``` [out] S ``` S is REAL array, dimension (min(M,N)) The singular values of A in decreasing order. The condition number of A in the 2-norm = S(1)/S(min(m,n)).``` [in] RCOND ``` RCOND is REAL RCOND is used to determine the effective rank of A. Singular values S(i) <= RCOND*S(1) are treated as zero. If RCOND < 0, machine precision is used instead.``` [out] RANK ``` RANK is INTEGER The effective rank of A, i.e., the number of singular values which are greater than RCOND*S(1).``` [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. LWORK must be at least 1. The exact minimum amount of workspace needed depends on M, N and NRHS. As long as LWORK is at least 12*N + 2*N*SMLSIZ + 8*N*NLVL + N*NRHS + (SMLSIZ+1)**2, if M is greater than or equal to N or 12*M + 2*M*SMLSIZ + 8*M*NLVL + M*NRHS + (SMLSIZ+1)**2, if M is less than N, the code will execute correctly. SMLSIZ is returned by ILAENV and is equal to the maximum size of the subproblems at the bottom of the computation tree (usually about 25), and NLVL = MAX( 0, INT( LOG_2( MIN( M,N )/(SMLSIZ+1) ) ) + 1 ) 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 array WORK and the minimum size of the array IWORK, and returns these values as the first entries of the WORK and IWORK arrays, and no error message related to LWORK is issued by XERBLA.``` [out] IWORK ``` IWORK is INTEGER array, dimension (MAX(1,LIWORK)) LIWORK >= max(1, 3*MINMN*NLVL + 11*MINMN), where MINMN = MIN( M,N ). On exit, if INFO = 0, IWORK(1) returns the minimum LIWORK.``` [out] INFO ``` INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value. > 0: the algorithm for computing the SVD failed to converge; if INFO = i, i off-diagonal elements of an intermediate bidiagonal form did not converge to zero.```
Contributors:
Ming Gu and Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA
Osni Marques, LBNL/NERSC, USA

Definition at line 208 of file sgelsd.f.

210 *
211 * -- LAPACK driver routine --
212 * -- LAPACK is a software package provided by Univ. of Tennessee, --
213 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
214 *
215 * .. Scalar Arguments ..
216  INTEGER INFO, LDA, LDB, LWORK, M, N, NRHS, RANK
217  REAL RCOND
218 * ..
219 * .. Array Arguments ..
220  INTEGER IWORK( * )
221  REAL A( LDA, * ), B( LDB, * ), S( * ), WORK( * )
222 * ..
223 *
224 * =====================================================================
225 *
226 * .. Parameters ..
227  REAL ZERO, ONE, TWO
228  parameter( zero = 0.0e0, one = 1.0e0, two = 2.0e0 )
229 * ..
230 * .. Local Scalars ..
231  LOGICAL LQUERY
232  INTEGER IASCL, IBSCL, IE, IL, ITAU, ITAUP, ITAUQ,
233  \$ LDWORK, LIWORK, MAXMN, MAXWRK, MINMN, MINWRK,
234  \$ MM, MNTHR, NLVL, NWORK, SMLSIZ, WLALSD
235  REAL ANRM, BIGNUM, BNRM, EPS, SFMIN, SMLNUM
236 * ..
237 * .. External Subroutines ..
238  EXTERNAL sgebrd, sgelqf, sgeqrf, slabad, slacpy, slalsd,
240 * ..
241 * .. External Functions ..
242  INTEGER ILAENV
243  REAL SLAMCH, SLANGE
244  EXTERNAL slamch, slange, ilaenv
245 * ..
246 * .. Intrinsic Functions ..
247  INTRINSIC int, log, max, min, real
248 * ..
249 * .. Executable Statements ..
250 *
251 * Test the input arguments.
252 *
253  info = 0
254  minmn = min( m, n )
255  maxmn = max( m, n )
256  lquery = ( lwork.EQ.-1 )
257  IF( m.LT.0 ) THEN
258  info = -1
259  ELSE IF( n.LT.0 ) THEN
260  info = -2
261  ELSE IF( nrhs.LT.0 ) THEN
262  info = -3
263  ELSE IF( lda.LT.max( 1, m ) ) THEN
264  info = -5
265  ELSE IF( ldb.LT.max( 1, maxmn ) ) THEN
266  info = -7
267  END IF
268 *
269 * Compute workspace.
270 * (Note: Comments in the code beginning "Workspace:" describe the
271 * minimal amount of workspace needed at that point in the code,
272 * as well as the preferred amount for good performance.
273 * NB refers to the optimal block size for the immediately
274 * following subroutine, as returned by ILAENV.)
275 *
276  IF( info.EQ.0 ) THEN
277  minwrk = 1
278  maxwrk = 1
279  liwork = 1
280  IF( minmn.GT.0 ) THEN
281  smlsiz = ilaenv( 9, 'SGELSD', ' ', 0, 0, 0, 0 )
282  mnthr = ilaenv( 6, 'SGELSD', ' ', m, n, nrhs, -1 )
283  nlvl = max( int( log( real( minmn ) / real( smlsiz + 1 ) ) /
284  \$ log( two ) ) + 1, 0 )
285  liwork = 3*minmn*nlvl + 11*minmn
286  mm = m
287  IF( m.GE.n .AND. m.GE.mnthr ) THEN
288 *
289 * Path 1a - overdetermined, with many more rows than
290 * columns.
291 *
292  mm = n
293  maxwrk = max( maxwrk, n + n*ilaenv( 1, 'SGEQRF', ' ', m,
294  \$ n, -1, -1 ) )
295  maxwrk = max( maxwrk, n + nrhs*ilaenv( 1, 'SORMQR', 'LT',
296  \$ m, nrhs, n, -1 ) )
297  END IF
298  IF( m.GE.n ) THEN
299 *
300 * Path 1 - overdetermined or exactly determined.
301 *
302  maxwrk = max( maxwrk, 3*n + ( mm + n )*ilaenv( 1,
303  \$ 'SGEBRD', ' ', mm, n, -1, -1 ) )
304  maxwrk = max( maxwrk, 3*n + nrhs*ilaenv( 1, 'SORMBR',
305  \$ 'QLT', mm, nrhs, n, -1 ) )
306  maxwrk = max( maxwrk, 3*n + ( n - 1 )*ilaenv( 1,
307  \$ 'SORMBR', 'PLN', n, nrhs, n, -1 ) )
308  wlalsd = 9*n + 2*n*smlsiz + 8*n*nlvl + n*nrhs +
309  \$ ( smlsiz + 1 )**2
310  maxwrk = max( maxwrk, 3*n + wlalsd )
311  minwrk = max( 3*n + mm, 3*n + nrhs, 3*n + wlalsd )
312  END IF
313  IF( n.GT.m ) THEN
314  wlalsd = 9*m + 2*m*smlsiz + 8*m*nlvl + m*nrhs +
315  \$ ( smlsiz + 1 )**2
316  IF( n.GE.mnthr ) THEN
317 *
318 * Path 2a - underdetermined, with many more columns
319 * than rows.
320 *
321  maxwrk = m + m*ilaenv( 1, 'SGELQF', ' ', m, n, -1,
322  \$ -1 )
323  maxwrk = max( maxwrk, m*m + 4*m + 2*m*ilaenv( 1,
324  \$ 'SGEBRD', ' ', m, m, -1, -1 ) )
325  maxwrk = max( maxwrk, m*m + 4*m + nrhs*ilaenv( 1,
326  \$ 'SORMBR', 'QLT', m, nrhs, m, -1 ) )
327  maxwrk = max( maxwrk, m*m + 4*m + ( m - 1 )*ilaenv( 1,
328  \$ 'SORMBR', 'PLN', m, nrhs, m, -1 ) )
329  IF( nrhs.GT.1 ) THEN
330  maxwrk = max( maxwrk, m*m + m + m*nrhs )
331  ELSE
332  maxwrk = max( maxwrk, m*m + 2*m )
333  END IF
334  maxwrk = max( maxwrk, m + nrhs*ilaenv( 1, 'SORMLQ',
335  \$ 'LT', n, nrhs, m, -1 ) )
336  maxwrk = max( maxwrk, m*m + 4*m + wlalsd )
337 ! XXX: Ensure the Path 2a case below is triggered. The workspace
338 ! calculation should use queries for all routines eventually.
339  maxwrk = max( maxwrk,
340  \$ 4*m+m*m+max( m, 2*m-4, nrhs, n-3*m ) )
341  ELSE
342 *
343 * Path 2 - remaining underdetermined cases.
344 *
345  maxwrk = 3*m + ( n + m )*ilaenv( 1, 'SGEBRD', ' ', m,
346  \$ n, -1, -1 )
347  maxwrk = max( maxwrk, 3*m + nrhs*ilaenv( 1, 'SORMBR',
348  \$ 'QLT', m, nrhs, n, -1 ) )
349  maxwrk = max( maxwrk, 3*m + m*ilaenv( 1, 'SORMBR',
350  \$ 'PLN', n, nrhs, m, -1 ) )
351  maxwrk = max( maxwrk, 3*m + wlalsd )
352  END IF
353  minwrk = max( 3*m + nrhs, 3*m + m, 3*m + wlalsd )
354  END IF
355  END IF
356  minwrk = min( minwrk, maxwrk )
357  work( 1 ) = maxwrk
358  iwork( 1 ) = liwork
359 *
360  IF( lwork.LT.minwrk .AND. .NOT.lquery ) THEN
361  info = -12
362  END IF
363  END IF
364 *
365  IF( info.NE.0 ) THEN
366  CALL xerbla( 'SGELSD', -info )
367  RETURN
368  ELSE IF( lquery ) THEN
369  RETURN
370  END IF
371 *
372 * Quick return if possible.
373 *
374  IF( m.EQ.0 .OR. n.EQ.0 ) THEN
375  rank = 0
376  RETURN
377  END IF
378 *
379 * Get machine parameters.
380 *
381  eps = slamch( 'P' )
382  sfmin = slamch( 'S' )
383  smlnum = sfmin / eps
384  bignum = one / smlnum
385  CALL slabad( smlnum, bignum )
386 *
387 * Scale A if max entry outside range [SMLNUM,BIGNUM].
388 *
389  anrm = slange( 'M', m, n, a, lda, work )
390  iascl = 0
391  IF( anrm.GT.zero .AND. anrm.LT.smlnum ) THEN
392 *
393 * Scale matrix norm up to SMLNUM.
394 *
395  CALL slascl( 'G', 0, 0, anrm, smlnum, m, n, a, lda, info )
396  iascl = 1
397  ELSE IF( anrm.GT.bignum ) THEN
398 *
399 * Scale matrix norm down to BIGNUM.
400 *
401  CALL slascl( 'G', 0, 0, anrm, bignum, m, n, a, lda, info )
402  iascl = 2
403  ELSE IF( anrm.EQ.zero ) THEN
404 *
405 * Matrix all zero. Return zero solution.
406 *
407  CALL slaset( 'F', max( m, n ), nrhs, zero, zero, b, ldb )
408  CALL slaset( 'F', minmn, 1, zero, zero, s, 1 )
409  rank = 0
410  GO TO 10
411  END IF
412 *
413 * Scale B if max entry outside range [SMLNUM,BIGNUM].
414 *
415  bnrm = slange( 'M', m, nrhs, b, ldb, work )
416  ibscl = 0
417  IF( bnrm.GT.zero .AND. bnrm.LT.smlnum ) THEN
418 *
419 * Scale matrix norm up to SMLNUM.
420 *
421  CALL slascl( 'G', 0, 0, bnrm, smlnum, m, nrhs, b, ldb, info )
422  ibscl = 1
423  ELSE IF( bnrm.GT.bignum ) THEN
424 *
425 * Scale matrix norm down to BIGNUM.
426 *
427  CALL slascl( 'G', 0, 0, bnrm, bignum, m, nrhs, b, ldb, info )
428  ibscl = 2
429  END IF
430 *
431 * If M < N make sure certain entries of B are zero.
432 *
433  IF( m.LT.n )
434  \$ CALL slaset( 'F', n-m, nrhs, zero, zero, b( m+1, 1 ), ldb )
435 *
436 * Overdetermined case.
437 *
438  IF( m.GE.n ) THEN
439 *
440 * Path 1 - overdetermined or exactly determined.
441 *
442  mm = m
443  IF( m.GE.mnthr ) THEN
444 *
445 * Path 1a - overdetermined, with many more rows than columns.
446 *
447  mm = n
448  itau = 1
449  nwork = itau + n
450 *
451 * Compute A=Q*R.
452 * (Workspace: need 2*N, prefer N+N*NB)
453 *
454  CALL sgeqrf( m, n, a, lda, work( itau ), work( nwork ),
455  \$ lwork-nwork+1, info )
456 *
457 * Multiply B by transpose(Q).
458 * (Workspace: need N+NRHS, prefer N+NRHS*NB)
459 *
460  CALL sormqr( 'L', 'T', m, nrhs, n, a, lda, work( itau ), b,
461  \$ ldb, work( nwork ), lwork-nwork+1, info )
462 *
463 * Zero out below R.
464 *
465  IF( n.GT.1 ) THEN
466  CALL slaset( 'L', n-1, n-1, zero, zero, a( 2, 1 ), lda )
467  END IF
468  END IF
469 *
470  ie = 1
471  itauq = ie + n
472  itaup = itauq + n
473  nwork = itaup + n
474 *
475 * Bidiagonalize R in A.
476 * (Workspace: need 3*N+MM, prefer 3*N+(MM+N)*NB)
477 *
478  CALL sgebrd( mm, n, a, lda, s, work( ie ), work( itauq ),
479  \$ work( itaup ), work( nwork ), lwork-nwork+1,
480  \$ info )
481 *
482 * Multiply B by transpose of left bidiagonalizing vectors of R.
483 * (Workspace: need 3*N+NRHS, prefer 3*N+NRHS*NB)
484 *
485  CALL sormbr( 'Q', 'L', 'T', mm, nrhs, n, a, lda, work( itauq ),
486  \$ b, ldb, work( nwork ), lwork-nwork+1, info )
487 *
488 * Solve the bidiagonal least squares problem.
489 *
490  CALL slalsd( 'U', smlsiz, n, nrhs, s, work( ie ), b, ldb,
491  \$ rcond, rank, work( nwork ), iwork, info )
492  IF( info.NE.0 ) THEN
493  GO TO 10
494  END IF
495 *
496 * Multiply B by right bidiagonalizing vectors of R.
497 *
498  CALL sormbr( 'P', 'L', 'N', n, nrhs, n, a, lda, work( itaup ),
499  \$ b, ldb, work( nwork ), lwork-nwork+1, info )
500 *
501  ELSE IF( n.GE.mnthr .AND. lwork.GE.4*m+m*m+
502  \$ max( m, 2*m-4, nrhs, n-3*m, wlalsd ) ) THEN
503 *
504 * Path 2a - underdetermined, with many more columns than rows
505 * and sufficient workspace for an efficient algorithm.
506 *
507  ldwork = m
508  IF( lwork.GE.max( 4*m+m*lda+max( m, 2*m-4, nrhs, n-3*m ),
509  \$ m*lda+m+m*nrhs, 4*m+m*lda+wlalsd ) )ldwork = lda
510  itau = 1
511  nwork = m + 1
512 *
513 * Compute A=L*Q.
514 * (Workspace: need 2*M, prefer M+M*NB)
515 *
516  CALL sgelqf( m, n, a, lda, work( itau ), work( nwork ),
517  \$ lwork-nwork+1, info )
518  il = nwork
519 *
520 * Copy L to WORK(IL), zeroing out above its diagonal.
521 *
522  CALL slacpy( 'L', m, m, a, lda, work( il ), ldwork )
523  CALL slaset( 'U', m-1, m-1, zero, zero, work( il+ldwork ),
524  \$ ldwork )
525  ie = il + ldwork*m
526  itauq = ie + m
527  itaup = itauq + m
528  nwork = itaup + m
529 *
530 * Bidiagonalize L in WORK(IL).
531 * (Workspace: need M*M+5*M, prefer M*M+4*M+2*M*NB)
532 *
533  CALL sgebrd( m, m, work( il ), ldwork, s, work( ie ),
534  \$ work( itauq ), work( itaup ), work( nwork ),
535  \$ lwork-nwork+1, info )
536 *
537 * Multiply B by transpose of left bidiagonalizing vectors of L.
538 * (Workspace: need M*M+4*M+NRHS, prefer M*M+4*M+NRHS*NB)
539 *
540  CALL sormbr( 'Q', 'L', 'T', m, nrhs, m, work( il ), ldwork,
541  \$ work( itauq ), b, ldb, work( nwork ),
542  \$ lwork-nwork+1, info )
543 *
544 * Solve the bidiagonal least squares problem.
545 *
546  CALL slalsd( 'U', smlsiz, m, nrhs, s, work( ie ), b, ldb,
547  \$ rcond, rank, work( nwork ), iwork, info )
548  IF( info.NE.0 ) THEN
549  GO TO 10
550  END IF
551 *
552 * Multiply B by right bidiagonalizing vectors of L.
553 *
554  CALL sormbr( 'P', 'L', 'N', m, nrhs, m, work( il ), ldwork,
555  \$ work( itaup ), b, ldb, work( nwork ),
556  \$ lwork-nwork+1, info )
557 *
558 * Zero out below first M rows of B.
559 *
560  CALL slaset( 'F', n-m, nrhs, zero, zero, b( m+1, 1 ), ldb )
561  nwork = itau + m
562 *
563 * Multiply transpose(Q) by B.
564 * (Workspace: need M+NRHS, prefer M+NRHS*NB)
565 *
566  CALL sormlq( 'L', 'T', n, nrhs, m, a, lda, work( itau ), b,
567  \$ ldb, work( nwork ), lwork-nwork+1, info )
568 *
569  ELSE
570 *
571 * Path 2 - remaining underdetermined cases.
572 *
573  ie = 1
574  itauq = ie + m
575  itaup = itauq + m
576  nwork = itaup + m
577 *
578 * Bidiagonalize A.
579 * (Workspace: need 3*M+N, prefer 3*M+(M+N)*NB)
580 *
581  CALL sgebrd( m, n, a, lda, s, work( ie ), work( itauq ),
582  \$ work( itaup ), work( nwork ), lwork-nwork+1,
583  \$ info )
584 *
585 * Multiply B by transpose of left bidiagonalizing vectors.
586 * (Workspace: need 3*M+NRHS, prefer 3*M+NRHS*NB)
587 *
588  CALL sormbr( 'Q', 'L', 'T', m, nrhs, n, a, lda, work( itauq ),
589  \$ b, ldb, work( nwork ), lwork-nwork+1, info )
590 *
591 * Solve the bidiagonal least squares problem.
592 *
593  CALL slalsd( 'L', smlsiz, m, nrhs, s, work( ie ), b, ldb,
594  \$ rcond, rank, work( nwork ), iwork, info )
595  IF( info.NE.0 ) THEN
596  GO TO 10
597  END IF
598 *
599 * Multiply B by right bidiagonalizing vectors of A.
600 *
601  CALL sormbr( 'P', 'L', 'N', n, nrhs, m, a, lda, work( itaup ),
602  \$ b, ldb, work( nwork ), lwork-nwork+1, info )
603 *
604  END IF
605 *
606 * Undo scaling.
607 *
608  IF( iascl.EQ.1 ) THEN
609  CALL slascl( 'G', 0, 0, anrm, smlnum, n, nrhs, b, ldb, info )
610  CALL slascl( 'G', 0, 0, smlnum, anrm, minmn, 1, s, minmn,
611  \$ info )
612  ELSE IF( iascl.EQ.2 ) THEN
613  CALL slascl( 'G', 0, 0, anrm, bignum, n, nrhs, b, ldb, info )
614  CALL slascl( 'G', 0, 0, bignum, anrm, minmn, 1, s, minmn,
615  \$ info )
616  END IF
617  IF( ibscl.EQ.1 ) THEN
618  CALL slascl( 'G', 0, 0, smlnum, bnrm, n, nrhs, b, ldb, info )
619  ELSE IF( ibscl.EQ.2 ) THEN
620  CALL slascl( 'G', 0, 0, bignum, bnrm, n, nrhs, b, ldb, info )
621  END IF
622 *
623  10 CONTINUE
624  work( 1 ) = maxwrk
625  iwork( 1 ) = liwork
626  RETURN
627 *
628 * End of SGELSD
629 *
subroutine slascl(TYPE, KL, KU, CFROM, CTO, M, N, A, LDA, INFO)
SLASCL multiplies a general rectangular matrix by a real scalar defined as cto/cfrom.
Definition: slascl.f:143
subroutine slaset(UPLO, M, N, ALPHA, BETA, A, LDA)
SLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
Definition: slaset.f:110
subroutine slacpy(UPLO, M, N, A, LDA, B, LDB)
SLACPY copies all or part of one two-dimensional array to another.
Definition: slacpy.f:103
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
ILAENV
Definition: ilaenv.f:162
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
real function slange(NORM, M, N, A, LDA, WORK)
SLANGE returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value ...
Definition: slange.f:114
subroutine sgeqrf(M, N, A, LDA, TAU, WORK, LWORK, INFO)
SGEQRF
Definition: sgeqrf.f:146
subroutine sgebrd(M, N, A, LDA, D, E, TAUQ, TAUP, WORK, LWORK, INFO)
SGEBRD
Definition: sgebrd.f:205
subroutine sgelqf(M, N, A, LDA, TAU, WORK, LWORK, INFO)
SGELQF
Definition: sgelqf.f:143
subroutine slalsd(UPLO, SMLSIZ, N, NRHS, D, E, B, LDB, RCOND, RANK, WORK, IWORK, INFO)
SLALSD uses the singular value decomposition of A to solve the least squares problem.
Definition: slalsd.f:179
subroutine sormbr(VECT, SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
SORMBR
Definition: sormbr.f:196
subroutine sormqr(SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
SORMQR
Definition: sormqr.f:168
subroutine sormlq(SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
SORMLQ
Definition: sormlq.f:168
real function slamch(CMACH)
SLAMCH
Definition: slamch.f:68
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