 LAPACK  3.10.0 LAPACK: Linear Algebra PACKage

## ◆ ztgsyl()

 subroutine ztgsyl ( character TRANS, integer IJOB, integer M, integer N, complex*16, dimension( lda, * ) A, integer LDA, complex*16, dimension( ldb, * ) B, integer LDB, complex*16, dimension( ldc, * ) C, integer LDC, complex*16, dimension( ldd, * ) D, integer LDD, complex*16, dimension( lde, * ) E, integer LDE, complex*16, dimension( ldf, * ) F, integer LDF, double precision SCALE, double precision DIF, complex*16, dimension( * ) WORK, integer LWORK, integer, dimension( * ) IWORK, integer INFO )

ZTGSYL

Purpose:
``` ZTGSYL solves the generalized Sylvester equation:

A * R - L * B = scale * C            (1)
D * R - L * E = scale * F

where R and L are unknown m-by-n matrices, (A, D), (B, E) and
(C, F) are given matrix pairs of size m-by-m, n-by-n and m-by-n,
respectively, with complex entries. A, B, D and E are upper
triangular (i.e., (A,D) and (B,E) in generalized Schur form).

The solution (R, L) overwrites (C, F). 0 <= SCALE <= 1
is an output scaling factor chosen to avoid overflow.

In matrix notation (1) is equivalent to solve Zx = scale*b, where Z
is defined as

Z = [ kron(In, A)  -kron(B**H, Im) ]        (2)
[ kron(In, D)  -kron(E**H, Im) ],

Here Ix is the identity matrix of size x and X**H is the conjugate
transpose of X. Kron(X, Y) is the Kronecker product between the
matrices X and Y.

If TRANS = 'C', y in the conjugate transposed system Z**H *y = scale*b
is solved for, which is equivalent to solve for R and L in

A**H * R + D**H * L = scale * C           (3)
R * B**H + L * E**H = scale * -F

This case (TRANS = 'C') is used to compute an one-norm-based estimate
of Dif[(A,D), (B,E)], the separation between the matrix pairs (A,D)
and (B,E), using ZLACON.

If IJOB >= 1, ZTGSYL computes a Frobenius norm-based estimate of
Dif[(A,D),(B,E)]. That is, the reciprocal of a lower bound on the
reciprocal of the smallest singular value of Z.

This is a level-3 BLAS algorithm.```
Parameters
 [in] TRANS ``` TRANS is CHARACTER*1 = 'N': solve the generalized sylvester equation (1). = 'C': solve the "conjugate transposed" system (3).``` [in] IJOB ``` IJOB is INTEGER Specifies what kind of functionality to be performed. =0: solve (1) only. =1: The functionality of 0 and 3. =2: The functionality of 0 and 4. =3: Only an estimate of Dif[(A,D), (B,E)] is computed. (look ahead strategy is used). =4: Only an estimate of Dif[(A,D), (B,E)] is computed. (ZGECON on sub-systems is used). Not referenced if TRANS = 'C'.``` [in] M ``` M is INTEGER The order of the matrices A and D, and the row dimension of the matrices C, F, R and L.``` [in] N ``` N is INTEGER The order of the matrices B and E, and the column dimension of the matrices C, F, R and L.``` [in] A ``` A is COMPLEX*16 array, dimension (LDA, M) The upper triangular matrix A.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1, M).``` [in] B ``` B is COMPLEX*16 array, dimension (LDB, N) The upper triangular matrix B.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1, N).``` [in,out] C ``` C is COMPLEX*16 array, dimension (LDC, N) On entry, C contains the right-hand-side of the first matrix equation in (1) or (3). On exit, if IJOB = 0, 1 or 2, C has been overwritten by the solution R. If IJOB = 3 or 4 and TRANS = 'N', C holds R, the solution achieved during the computation of the Dif-estimate.``` [in] LDC ``` LDC is INTEGER The leading dimension of the array C. LDC >= max(1, M).``` [in] D ``` D is COMPLEX*16 array, dimension (LDD, M) The upper triangular matrix D.``` [in] LDD ``` LDD is INTEGER The leading dimension of the array D. LDD >= max(1, M).``` [in] E ``` E is COMPLEX*16 array, dimension (LDE, N) The upper triangular matrix E.``` [in] LDE ``` LDE is INTEGER The leading dimension of the array E. LDE >= max(1, N).``` [in,out] F ``` F is COMPLEX*16 array, dimension (LDF, N) On entry, F contains the right-hand-side of the second matrix equation in (1) or (3). On exit, if IJOB = 0, 1 or 2, F has been overwritten by the solution L. If IJOB = 3 or 4 and TRANS = 'N', F holds L, the solution achieved during the computation of the Dif-estimate.``` [in] LDF ``` LDF is INTEGER The leading dimension of the array F. LDF >= max(1, M).``` [out] DIF ``` DIF is DOUBLE PRECISION On exit DIF is the reciprocal of a lower bound of the reciprocal of the Dif-function, i.e. DIF is an upper bound of Dif[(A,D), (B,E)] = sigma-min(Z), where Z as in (2). IF IJOB = 0 or TRANS = 'C', DIF is not referenced.``` [out] SCALE ``` SCALE is DOUBLE PRECISION On exit SCALE is the scaling factor in (1) or (3). If 0 < SCALE < 1, C and F hold the solutions R and L, resp., to a slightly perturbed system but the input matrices A, B, D and E have not been changed. If SCALE = 0, R and L will hold the solutions to the homogeneous system with C = F = 0.``` [out] WORK ``` WORK is COMPLEX*16 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 > = 1. If IJOB = 1 or 2 and TRANS = 'N', LWORK >= max(1,2*M*N). 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] IWORK ` IWORK is INTEGER array, dimension (M+N+2)` [out] INFO ``` INFO is INTEGER =0: successful exit <0: If INFO = -i, the i-th argument had an illegal value. >0: (A, D) and (B, E) have common or very close eigenvalues.```
Contributors:
Bo Kagstrom and Peter Poromaa, Department of Computing Science, Umea University, S-901 87 Umea, Sweden.
References:
 B. Kagstrom and P. Poromaa, LAPACK-Style Algorithms and Software for Solving the Generalized Sylvester Equation and Estimating the Separation between Regular Matrix Pairs, Report UMINF - 93.23, Department of Computing Science, Umea University, S-901 87 Umea, Sweden, December 1993, Revised April 1994, Also as LAPACK Working Note 75. To appear in ACM Trans. on Math. Software, Vol 22, No 1, 1996.
 B. Kagstrom, A Perturbation Analysis of the Generalized Sylvester Equation (AR - LB, DR - LE ) = (C, F), SIAM J. Matrix Anal. Appl., 15(4):1045-1060, 1994.
 B. Kagstrom and L. Westin, Generalized Schur Methods with Condition Estimators for Solving the Generalized Sylvester Equation, IEEE Transactions on Automatic Control, Vol. 34, No. 7, July 1989, pp 745-751.

Definition at line 292 of file ztgsyl.f.

295 *
296 * -- LAPACK computational routine --
297 * -- LAPACK is a software package provided by Univ. of Tennessee, --
298 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
299 *
300 * .. Scalar Arguments ..
301  CHARACTER TRANS
302  INTEGER IJOB, INFO, LDA, LDB, LDC, LDD, LDE, LDF,
303  \$ LWORK, M, N
304  DOUBLE PRECISION DIF, SCALE
305 * ..
306 * .. Array Arguments ..
307  INTEGER IWORK( * )
308  COMPLEX*16 A( LDA, * ), B( LDB, * ), C( LDC, * ),
309  \$ D( LDD, * ), E( LDE, * ), F( LDF, * ),
310  \$ WORK( * )
311 * ..
312 *
313 * =====================================================================
314 * Replaced various illegal calls to CCOPY by calls to CLASET.
315 * Sven Hammarling, 1/5/02.
316 *
317 * .. Parameters ..
318  DOUBLE PRECISION ZERO, ONE
319  parameter( zero = 0.0d+0, one = 1.0d+0 )
320  COMPLEX*16 CZERO
321  parameter( czero = (0.0d+0, 0.0d+0) )
322 * ..
323 * .. Local Scalars ..
324  LOGICAL LQUERY, NOTRAN
325  INTEGER I, IE, IFUNC, IROUND, IS, ISOLVE, J, JE, JS, K,
326  \$ LINFO, LWMIN, MB, NB, P, PQ, Q
327  DOUBLE PRECISION DSCALE, DSUM, SCALE2, SCALOC
328 * ..
329 * .. External Functions ..
330  LOGICAL LSAME
331  INTEGER ILAENV
332  EXTERNAL lsame, ilaenv
333 * ..
334 * .. External Subroutines ..
335  EXTERNAL xerbla, zgemm, zlacpy, zlaset, zscal, ztgsy2
336 * ..
337 * .. Intrinsic Functions ..
338  INTRINSIC dble, dcmplx, max, sqrt
339 * ..
340 * .. Executable Statements ..
341 *
342 * Decode and test input parameters
343 *
344  info = 0
345  notran = lsame( trans, 'N' )
346  lquery = ( lwork.EQ.-1 )
347 *
348  IF( .NOT.notran .AND. .NOT.lsame( trans, 'C' ) ) THEN
349  info = -1
350  ELSE IF( notran ) THEN
351  IF( ( ijob.LT.0 ) .OR. ( ijob.GT.4 ) ) THEN
352  info = -2
353  END IF
354  END IF
355  IF( info.EQ.0 ) THEN
356  IF( m.LE.0 ) THEN
357  info = -3
358  ELSE IF( n.LE.0 ) THEN
359  info = -4
360  ELSE IF( lda.LT.max( 1, m ) ) THEN
361  info = -6
362  ELSE IF( ldb.LT.max( 1, n ) ) THEN
363  info = -8
364  ELSE IF( ldc.LT.max( 1, m ) ) THEN
365  info = -10
366  ELSE IF( ldd.LT.max( 1, m ) ) THEN
367  info = -12
368  ELSE IF( lde.LT.max( 1, n ) ) THEN
369  info = -14
370  ELSE IF( ldf.LT.max( 1, m ) ) THEN
371  info = -16
372  END IF
373  END IF
374 *
375  IF( info.EQ.0 ) THEN
376  IF( notran ) THEN
377  IF( ijob.EQ.1 .OR. ijob.EQ.2 ) THEN
378  lwmin = max( 1, 2*m*n )
379  ELSE
380  lwmin = 1
381  END IF
382  ELSE
383  lwmin = 1
384  END IF
385  work( 1 ) = lwmin
386 *
387  IF( lwork.LT.lwmin .AND. .NOT.lquery ) THEN
388  info = -20
389  END IF
390  END IF
391 *
392  IF( info.NE.0 ) THEN
393  CALL xerbla( 'ZTGSYL', -info )
394  RETURN
395  ELSE IF( lquery ) THEN
396  RETURN
397  END IF
398 *
399 * Quick return if possible
400 *
401  IF( m.EQ.0 .OR. n.EQ.0 ) THEN
402  scale = 1
403  IF( notran ) THEN
404  IF( ijob.NE.0 ) THEN
405  dif = 0
406  END IF
407  END IF
408  RETURN
409  END IF
410 *
411 * Determine optimal block sizes MB and NB
412 *
413  mb = ilaenv( 2, 'ZTGSYL', trans, m, n, -1, -1 )
414  nb = ilaenv( 5, 'ZTGSYL', trans, m, n, -1, -1 )
415 *
416  isolve = 1
417  ifunc = 0
418  IF( notran ) THEN
419  IF( ijob.GE.3 ) THEN
420  ifunc = ijob - 2
421  CALL zlaset( 'F', m, n, czero, czero, c, ldc )
422  CALL zlaset( 'F', m, n, czero, czero, f, ldf )
423  ELSE IF( ijob.GE.1 .AND. notran ) THEN
424  isolve = 2
425  END IF
426  END IF
427 *
428  IF( ( mb.LE.1 .AND. nb.LE.1 ) .OR. ( mb.GE.m .AND. nb.GE.n ) )
429  \$ THEN
430 *
431 * Use unblocked Level 2 solver
432 *
433  DO 30 iround = 1, isolve
434 *
435  scale = one
436  dscale = zero
437  dsum = one
438  pq = m*n
439  CALL ztgsy2( trans, ifunc, m, n, a, lda, b, ldb, c, ldc, d,
440  \$ ldd, e, lde, f, ldf, scale, dsum, dscale,
441  \$ info )
442  IF( dscale.NE.zero ) THEN
443  IF( ijob.EQ.1 .OR. ijob.EQ.3 ) THEN
444  dif = sqrt( dble( 2*m*n ) ) / ( dscale*sqrt( dsum ) )
445  ELSE
446  dif = sqrt( dble( pq ) ) / ( dscale*sqrt( dsum ) )
447  END IF
448  END IF
449  IF( isolve.EQ.2 .AND. iround.EQ.1 ) THEN
450  IF( notran ) THEN
451  ifunc = ijob
452  END IF
453  scale2 = scale
454  CALL zlacpy( 'F', m, n, c, ldc, work, m )
455  CALL zlacpy( 'F', m, n, f, ldf, work( m*n+1 ), m )
456  CALL zlaset( 'F', m, n, czero, czero, c, ldc )
457  CALL zlaset( 'F', m, n, czero, czero, f, ldf )
458  ELSE IF( isolve.EQ.2 .AND. iround.EQ.2 ) THEN
459  CALL zlacpy( 'F', m, n, work, m, c, ldc )
460  CALL zlacpy( 'F', m, n, work( m*n+1 ), m, f, ldf )
461  scale = scale2
462  END IF
463  30 CONTINUE
464 *
465  RETURN
466 *
467  END IF
468 *
469 * Determine block structure of A
470 *
471  p = 0
472  i = 1
473  40 CONTINUE
474  IF( i.GT.m )
475  \$ GO TO 50
476  p = p + 1
477  iwork( p ) = i
478  i = i + mb
479  IF( i.GE.m )
480  \$ GO TO 50
481  GO TO 40
482  50 CONTINUE
483  iwork( p+1 ) = m + 1
484  IF( iwork( p ).EQ.iwork( p+1 ) )
485  \$ p = p - 1
486 *
487 * Determine block structure of B
488 *
489  q = p + 1
490  j = 1
491  60 CONTINUE
492  IF( j.GT.n )
493  \$ GO TO 70
494 *
495  q = q + 1
496  iwork( q ) = j
497  j = j + nb
498  IF( j.GE.n )
499  \$ GO TO 70
500  GO TO 60
501 *
502  70 CONTINUE
503  iwork( q+1 ) = n + 1
504  IF( iwork( q ).EQ.iwork( q+1 ) )
505  \$ q = q - 1
506 *
507  IF( notran ) THEN
508  DO 150 iround = 1, isolve
509 *
510 * Solve (I, J) - subsystem
511 * A(I, I) * R(I, J) - L(I, J) * B(J, J) = C(I, J)
512 * D(I, I) * R(I, J) - L(I, J) * E(J, J) = F(I, J)
513 * for I = P, P - 1, ..., 1; J = 1, 2, ..., Q
514 *
515  pq = 0
516  scale = one
517  dscale = zero
518  dsum = one
519  DO 130 j = p + 2, q
520  js = iwork( j )
521  je = iwork( j+1 ) - 1
522  nb = je - js + 1
523  DO 120 i = p, 1, -1
524  is = iwork( i )
525  ie = iwork( i+1 ) - 1
526  mb = ie - is + 1
527  CALL ztgsy2( trans, ifunc, mb, nb, a( is, is ), lda,
528  \$ b( js, js ), ldb, c( is, js ), ldc,
529  \$ d( is, is ), ldd, e( js, js ), lde,
530  \$ f( is, js ), ldf, scaloc, dsum, dscale,
531  \$ linfo )
532  IF( linfo.GT.0 )
533  \$ info = linfo
534  pq = pq + mb*nb
535  IF( scaloc.NE.one ) THEN
536  DO 80 k = 1, js - 1
537  CALL zscal( m, dcmplx( scaloc, zero ),
538  \$ c( 1, k ), 1 )
539  CALL zscal( m, dcmplx( scaloc, zero ),
540  \$ f( 1, k ), 1 )
541  80 CONTINUE
542  DO 90 k = js, je
543  CALL zscal( is-1, dcmplx( scaloc, zero ),
544  \$ c( 1, k ), 1 )
545  CALL zscal( is-1, dcmplx( scaloc, zero ),
546  \$ f( 1, k ), 1 )
547  90 CONTINUE
548  DO 100 k = js, je
549  CALL zscal( m-ie, dcmplx( scaloc, zero ),
550  \$ c( ie+1, k ), 1 )
551  CALL zscal( m-ie, dcmplx( scaloc, zero ),
552  \$ f( ie+1, k ), 1 )
553  100 CONTINUE
554  DO 110 k = je + 1, n
555  CALL zscal( m, dcmplx( scaloc, zero ),
556  \$ c( 1, k ), 1 )
557  CALL zscal( m, dcmplx( scaloc, zero ),
558  \$ f( 1, k ), 1 )
559  110 CONTINUE
560  scale = scale*scaloc
561  END IF
562 *
563 * Substitute R(I,J) and L(I,J) into remaining equation.
564 *
565  IF( i.GT.1 ) THEN
566  CALL zgemm( 'N', 'N', is-1, nb, mb,
567  \$ dcmplx( -one, zero ), a( 1, is ), lda,
568  \$ c( is, js ), ldc, dcmplx( one, zero ),
569  \$ c( 1, js ), ldc )
570  CALL zgemm( 'N', 'N', is-1, nb, mb,
571  \$ dcmplx( -one, zero ), d( 1, is ), ldd,
572  \$ c( is, js ), ldc, dcmplx( one, zero ),
573  \$ f( 1, js ), ldf )
574  END IF
575  IF( j.LT.q ) THEN
576  CALL zgemm( 'N', 'N', mb, n-je, nb,
577  \$ dcmplx( one, zero ), f( is, js ), ldf,
578  \$ b( js, je+1 ), ldb,
579  \$ dcmplx( one, zero ), c( is, je+1 ),
580  \$ ldc )
581  CALL zgemm( 'N', 'N', mb, n-je, nb,
582  \$ dcmplx( one, zero ), f( is, js ), ldf,
583  \$ e( js, je+1 ), lde,
584  \$ dcmplx( one, zero ), f( is, je+1 ),
585  \$ ldf )
586  END IF
587  120 CONTINUE
588  130 CONTINUE
589  IF( dscale.NE.zero ) THEN
590  IF( ijob.EQ.1 .OR. ijob.EQ.3 ) THEN
591  dif = sqrt( dble( 2*m*n ) ) / ( dscale*sqrt( dsum ) )
592  ELSE
593  dif = sqrt( dble( pq ) ) / ( dscale*sqrt( dsum ) )
594  END IF
595  END IF
596  IF( isolve.EQ.2 .AND. iround.EQ.1 ) THEN
597  IF( notran ) THEN
598  ifunc = ijob
599  END IF
600  scale2 = scale
601  CALL zlacpy( 'F', m, n, c, ldc, work, m )
602  CALL zlacpy( 'F', m, n, f, ldf, work( m*n+1 ), m )
603  CALL zlaset( 'F', m, n, czero, czero, c, ldc )
604  CALL zlaset( 'F', m, n, czero, czero, f, ldf )
605  ELSE IF( isolve.EQ.2 .AND. iround.EQ.2 ) THEN
606  CALL zlacpy( 'F', m, n, work, m, c, ldc )
607  CALL zlacpy( 'F', m, n, work( m*n+1 ), m, f, ldf )
608  scale = scale2
609  END IF
610  150 CONTINUE
611  ELSE
612 *
613 * Solve transposed (I, J)-subsystem
614 * A(I, I)**H * R(I, J) + D(I, I)**H * L(I, J) = C(I, J)
615 * R(I, J) * B(J, J) + L(I, J) * E(J, J) = -F(I, J)
616 * for I = 1,2,..., P; J = Q, Q-1,..., 1
617 *
618  scale = one
619  DO 210 i = 1, p
620  is = iwork( i )
621  ie = iwork( i+1 ) - 1
622  mb = ie - is + 1
623  DO 200 j = q, p + 2, -1
624  js = iwork( j )
625  je = iwork( j+1 ) - 1
626  nb = je - js + 1
627  CALL ztgsy2( trans, ifunc, mb, nb, a( is, is ), lda,
628  \$ b( js, js ), ldb, c( is, js ), ldc,
629  \$ d( is, is ), ldd, e( js, js ), lde,
630  \$ f( is, js ), ldf, scaloc, dsum, dscale,
631  \$ linfo )
632  IF( linfo.GT.0 )
633  \$ info = linfo
634  IF( scaloc.NE.one ) THEN
635  DO 160 k = 1, js - 1
636  CALL zscal( m, dcmplx( scaloc, zero ), c( 1, k ),
637  \$ 1 )
638  CALL zscal( m, dcmplx( scaloc, zero ), f( 1, k ),
639  \$ 1 )
640  160 CONTINUE
641  DO 170 k = js, je
642  CALL zscal( is-1, dcmplx( scaloc, zero ),
643  \$ c( 1, k ), 1 )
644  CALL zscal( is-1, dcmplx( scaloc, zero ),
645  \$ f( 1, k ), 1 )
646  170 CONTINUE
647  DO 180 k = js, je
648  CALL zscal( m-ie, dcmplx( scaloc, zero ),
649  \$ c( ie+1, k ), 1 )
650  CALL zscal( m-ie, dcmplx( scaloc, zero ),
651  \$ f( ie+1, k ), 1 )
652  180 CONTINUE
653  DO 190 k = je + 1, n
654  CALL zscal( m, dcmplx( scaloc, zero ), c( 1, k ),
655  \$ 1 )
656  CALL zscal( m, dcmplx( scaloc, zero ), f( 1, k ),
657  \$ 1 )
658  190 CONTINUE
659  scale = scale*scaloc
660  END IF
661 *
662 * Substitute R(I,J) and L(I,J) into remaining equation.
663 *
664  IF( j.GT.p+2 ) THEN
665  CALL zgemm( 'N', 'C', mb, js-1, nb,
666  \$ dcmplx( one, zero ), c( is, js ), ldc,
667  \$ b( 1, js ), ldb, dcmplx( one, zero ),
668  \$ f( is, 1 ), ldf )
669  CALL zgemm( 'N', 'C', mb, js-1, nb,
670  \$ dcmplx( one, zero ), f( is, js ), ldf,
671  \$ e( 1, js ), lde, dcmplx( one, zero ),
672  \$ f( is, 1 ), ldf )
673  END IF
674  IF( i.LT.p ) THEN
675  CALL zgemm( 'C', 'N', m-ie, nb, mb,
676  \$ dcmplx( -one, zero ), a( is, ie+1 ), lda,
677  \$ c( is, js ), ldc, dcmplx( one, zero ),
678  \$ c( ie+1, js ), ldc )
679  CALL zgemm( 'C', 'N', m-ie, nb, mb,
680  \$ dcmplx( -one, zero ), d( is, ie+1 ), ldd,
681  \$ f( is, js ), ldf, dcmplx( one, zero ),
682  \$ c( ie+1, js ), ldc )
683  END IF
684  200 CONTINUE
685  210 CONTINUE
686  END IF
687 *
688  work( 1 ) = lwmin
689 *
690  RETURN
691 *
692 * End of ZTGSYL
693 *
logical function lde(RI, RJ, LR)
Definition: dblat2.f:2942
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
ILAENV
Definition: ilaenv.f:162
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine zscal(N, ZA, ZX, INCX)
ZSCAL
Definition: zscal.f:78
subroutine zgemm(TRANSA, TRANSB, M, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
ZGEMM
Definition: zgemm.f:187
subroutine zlacpy(UPLO, M, N, A, LDA, B, LDB)
ZLACPY copies all or part of one two-dimensional array to another.
Definition: zlacpy.f:103
subroutine zlaset(UPLO, M, N, ALPHA, BETA, A, LDA)
ZLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
Definition: zlaset.f:106
subroutine ztgsy2(TRANS, IJOB, M, N, A, LDA, B, LDB, C, LDC, D, LDD, E, LDE, F, LDF, SCALE, RDSUM, RDSCAL, INFO)
ZTGSY2 solves the generalized Sylvester equation (unblocked algorithm).
Definition: ztgsy2.f:259
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