LAPACK 3.12.0 LAPACK: Linear Algebra PACKage
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## ◆ zlavsy()

 subroutine zlavsy ( character uplo, character trans, character diag, integer n, integer nrhs, complex*16, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, complex*16, dimension( ldb, * ) b, integer ldb, integer info )

ZLAVSY

Purpose:
``` ZLAVSY performs one of the matrix-vector operations
x := A*x  or  x := A'*x,
where x is an N element vector and  A is one of the factors
from the block U*D*U' or L*D*L' factorization computed by ZSYTRF.

If TRANS = 'N', multiplies by U  or U * D  (or L  or L * D)
If TRANS = 'T', multiplies by U' or D * U' (or L' or D * L')```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 Specifies whether the factor stored in A is upper or lower triangular. = 'U': Upper triangular = 'L': Lower triangular``` [in] TRANS ``` TRANS is CHARACTER*1 Specifies the operation to be performed: = 'N': x := A*x = 'T': x := A'*x``` [in] DIAG ``` DIAG is CHARACTER*1 Specifies whether or not the diagonal blocks are unit matrices. If the diagonal blocks are assumed to be unit, then A = U or A = L, otherwise A = U*D or A = L*D. = 'U': Diagonal blocks are assumed to be unit matrices. = 'N': Diagonal blocks are assumed to be non-unit matrices.``` [in] N ``` N is INTEGER The number of rows and columns of the matrix A. N >= 0.``` [in] NRHS ``` NRHS is INTEGER The number of right hand sides, i.e., the number of vectors x to be multiplied by A. NRHS >= 0.``` [in] A ``` A is COMPLEX*16 array, dimension (LDA,N) The block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by ZSYTRF. Stored as a 2-D triangular matrix.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).``` [in] IPIV ``` IPIV is INTEGER array, dimension (N) Details of the interchanges and the block structure of D, as determined by ZSYTRF. If UPLO = 'U': If IPIV(k) > 0, then rows and columns k and IPIV(k) were interchanged and D(k,k) is a 1-by-1 diagonal block. (If IPIV( k ) = k, no interchange was done). If IPIV(k) = IPIV(k-1) < 0, then rows and columns k-1 and -IPIV(k) were interchanged, D(k-1:k,k-1:k) is a 2-by-2 diagonal block. If UPLO = 'L': If IPIV(k) > 0, then rows and columns k and IPIV(k) were interchanged and D(k,k) is a 1-by-1 diagonal block. (If IPIV( k ) = k, no interchange was done). If IPIV(k) = IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were interchanged, D(k:k+1,k:k+1) is a 2-by-2 diagonal block.``` [in,out] B ``` B is COMPLEX*16 array, dimension (LDB,NRHS) On entry, B contains NRHS vectors of length N. On exit, B is overwritten with the product A * B.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N).``` [out] INFO ``` INFO is INTEGER = 0: successful exit < 0: if INFO = -k, the k-th argument had an illegal value```

Definition at line 151 of file zlavsy.f.

153*
154* -- LAPACK test routine --
155* -- LAPACK is a software package provided by Univ. of Tennessee, --
156* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
157*
158* .. Scalar Arguments ..
159 CHARACTER DIAG, TRANS, UPLO
160 INTEGER INFO, LDA, LDB, N, NRHS
161* ..
162* .. Array Arguments ..
163 INTEGER IPIV( * )
164 COMPLEX*16 A( LDA, * ), B( LDB, * )
165* ..
166*
167* =====================================================================
168*
169* .. Parameters ..
170 COMPLEX*16 CONE
171 parameter( cone = ( 1.0d+0, 0.0d+0 ) )
172* ..
173* .. Local Scalars ..
174 LOGICAL NOUNIT
175 INTEGER J, K, KP
176 COMPLEX*16 D11, D12, D21, D22, T1, T2
177* ..
178* .. External Functions ..
179 LOGICAL LSAME
180 EXTERNAL lsame
181* ..
182* .. External Subroutines ..
183 EXTERNAL xerbla, zgemv, zgeru, zscal, zswap
184* ..
185* .. Intrinsic Functions ..
186 INTRINSIC abs, max
187* ..
188* .. Executable Statements ..
189*
190* Test the input parameters.
191*
192 info = 0
193 IF( .NOT.lsame( uplo, 'U' ) .AND. .NOT.lsame( uplo, 'L' ) ) THEN
194 info = -1
195 ELSE IF( .NOT.lsame( trans, 'N' ) .AND. .NOT.lsame( trans, 'T' ) )
196 \$ THEN
197 info = -2
198 ELSE IF( .NOT.lsame( diag, 'U' ) .AND. .NOT.lsame( diag, 'N' ) )
199 \$ THEN
200 info = -3
201 ELSE IF( n.LT.0 ) THEN
202 info = -4
203 ELSE IF( lda.LT.max( 1, n ) ) THEN
204 info = -6
205 ELSE IF( ldb.LT.max( 1, n ) ) THEN
206 info = -9
207 END IF
208 IF( info.NE.0 ) THEN
209 CALL xerbla( 'ZLAVSY ', -info )
210 RETURN
211 END IF
212*
213* Quick return if possible.
214*
215 IF( n.EQ.0 )
216 \$ RETURN
217*
218 nounit = lsame( diag, 'N' )
219*------------------------------------------
220*
221* Compute B := A * B (No transpose)
222*
223*------------------------------------------
224 IF( lsame( trans, 'N' ) ) THEN
225*
226* Compute B := U*B
227* where U = P(m)*inv(U(m))* ... *P(1)*inv(U(1))
228*
229 IF( lsame( uplo, 'U' ) ) THEN
230*
231* Loop forward applying the transformations.
232*
233 k = 1
234 10 CONTINUE
235 IF( k.GT.n )
236 \$ GO TO 30
237 IF( ipiv( k ).GT.0 ) THEN
238*
239* 1 x 1 pivot block
240*
241* Multiply by the diagonal element if forming U * D.
242*
243 IF( nounit )
244 \$ CALL zscal( nrhs, a( k, k ), b( k, 1 ), ldb )
245*
246* Multiply by P(K) * inv(U(K)) if K > 1.
247*
248 IF( k.GT.1 ) THEN
249*
250* Apply the transformation.
251*
252 CALL zgeru( k-1, nrhs, cone, a( 1, k ), 1, b( k, 1 ),
253 \$ ldb, b( 1, 1 ), ldb )
254*
255* Interchange if P(K) != I.
256*
257 kp = ipiv( k )
258 IF( kp.NE.k )
259 \$ CALL zswap( nrhs, b( k, 1 ), ldb, b( kp, 1 ), ldb )
260 END IF
261 k = k + 1
262 ELSE
263*
264* 2 x 2 pivot block
265*
266* Multiply by the diagonal block if forming U * D.
267*
268 IF( nounit ) THEN
269 d11 = a( k, k )
270 d22 = a( k+1, k+1 )
271 d12 = a( k, k+1 )
272 d21 = d12
273 DO 20 j = 1, nrhs
274 t1 = b( k, j )
275 t2 = b( k+1, j )
276 b( k, j ) = d11*t1 + d12*t2
277 b( k+1, j ) = d21*t1 + d22*t2
278 20 CONTINUE
279 END IF
280*
281* Multiply by P(K) * inv(U(K)) if K > 1.
282*
283 IF( k.GT.1 ) THEN
284*
285* Apply the transformations.
286*
287 CALL zgeru( k-1, nrhs, cone, a( 1, k ), 1, b( k, 1 ),
288 \$ ldb, b( 1, 1 ), ldb )
289 CALL zgeru( k-1, nrhs, cone, a( 1, k+1 ), 1,
290 \$ b( k+1, 1 ), ldb, b( 1, 1 ), ldb )
291*
292* Interchange if P(K) != I.
293*
294 kp = abs( ipiv( k ) )
295 IF( kp.NE.k )
296 \$ CALL zswap( nrhs, b( k, 1 ), ldb, b( kp, 1 ), ldb )
297 END IF
298 k = k + 2
299 END IF
300 GO TO 10
301 30 CONTINUE
302*
303* Compute B := L*B
304* where L = P(1)*inv(L(1))* ... *P(m)*inv(L(m)) .
305*
306 ELSE
307*
308* Loop backward applying the transformations to B.
309*
310 k = n
311 40 CONTINUE
312 IF( k.LT.1 )
313 \$ GO TO 60
314*
315* Test the pivot index. If greater than zero, a 1 x 1
316* pivot was used, otherwise a 2 x 2 pivot was used.
317*
318 IF( ipiv( k ).GT.0 ) THEN
319*
320* 1 x 1 pivot block:
321*
322* Multiply by the diagonal element if forming L * D.
323*
324 IF( nounit )
325 \$ CALL zscal( nrhs, a( k, k ), b( k, 1 ), ldb )
326*
327* Multiply by P(K) * inv(L(K)) if K < N.
328*
329 IF( k.NE.n ) THEN
330 kp = ipiv( k )
331*
332* Apply the transformation.
333*
334 CALL zgeru( n-k, nrhs, cone, a( k+1, k ), 1,
335 \$ b( k, 1 ), ldb, b( k+1, 1 ), ldb )
336*
337* Interchange if a permutation was applied at the
338* K-th step of the factorization.
339*
340 IF( kp.NE.k )
341 \$ CALL zswap( nrhs, b( k, 1 ), ldb, b( kp, 1 ), ldb )
342 END IF
343 k = k - 1
344*
345 ELSE
346*
347* 2 x 2 pivot block:
348*
349* Multiply by the diagonal block if forming L * D.
350*
351 IF( nounit ) THEN
352 d11 = a( k-1, k-1 )
353 d22 = a( k, k )
354 d21 = a( k, k-1 )
355 d12 = d21
356 DO 50 j = 1, nrhs
357 t1 = b( k-1, j )
358 t2 = b( k, j )
359 b( k-1, j ) = d11*t1 + d12*t2
360 b( k, j ) = d21*t1 + d22*t2
361 50 CONTINUE
362 END IF
363*
364* Multiply by P(K) * inv(L(K)) if K < N.
365*
366 IF( k.NE.n ) THEN
367*
368* Apply the transformation.
369*
370 CALL zgeru( n-k, nrhs, cone, a( k+1, k ), 1,
371 \$ b( k, 1 ), ldb, b( k+1, 1 ), ldb )
372 CALL zgeru( n-k, nrhs, cone, a( k+1, k-1 ), 1,
373 \$ b( k-1, 1 ), ldb, b( k+1, 1 ), ldb )
374*
375* Interchange if a permutation was applied at the
376* K-th step of the factorization.
377*
378 kp = abs( ipiv( k ) )
379 IF( kp.NE.k )
380 \$ CALL zswap( nrhs, b( k, 1 ), ldb, b( kp, 1 ), ldb )
381 END IF
382 k = k - 2
383 END IF
384 GO TO 40
385 60 CONTINUE
386 END IF
387*----------------------------------------
388*
389* Compute B := A' * B (transpose)
390*
391*----------------------------------------
392 ELSE IF( lsame( trans, 'T' ) ) THEN
393*
394* Form B := U'*B
395* where U = P(m)*inv(U(m))* ... *P(1)*inv(U(1))
396* and U' = inv(U'(1))*P(1)* ... *inv(U'(m))*P(m)
397*
398 IF( lsame( uplo, 'U' ) ) THEN
399*
400* Loop backward applying the transformations.
401*
402 k = n
403 70 CONTINUE
404 IF( k.LT.1 )
405 \$ GO TO 90
406*
407* 1 x 1 pivot block.
408*
409 IF( ipiv( k ).GT.0 ) THEN
410 IF( k.GT.1 ) THEN
411*
412* Interchange if P(K) != I.
413*
414 kp = ipiv( k )
415 IF( kp.NE.k )
416 \$ CALL zswap( nrhs, b( k, 1 ), ldb, b( kp, 1 ), ldb )
417*
418* Apply the transformation
419*
420 CALL zgemv( 'Transpose', k-1, nrhs, cone, b, ldb,
421 \$ a( 1, k ), 1, cone, b( k, 1 ), ldb )
422 END IF
423 IF( nounit )
424 \$ CALL zscal( nrhs, a( k, k ), b( k, 1 ), ldb )
425 k = k - 1
426*
427* 2 x 2 pivot block.
428*
429 ELSE
430 IF( k.GT.2 ) THEN
431*
432* Interchange if P(K) != I.
433*
434 kp = abs( ipiv( k ) )
435 IF( kp.NE.k-1 )
436 \$ CALL zswap( nrhs, b( k-1, 1 ), ldb, b( kp, 1 ),
437 \$ ldb )
438*
439* Apply the transformations
440*
441 CALL zgemv( 'Transpose', k-2, nrhs, cone, b, ldb,
442 \$ a( 1, k ), 1, cone, b( k, 1 ), ldb )
443 CALL zgemv( 'Transpose', k-2, nrhs, cone, b, ldb,
444 \$ a( 1, k-1 ), 1, cone, b( k-1, 1 ), ldb )
445 END IF
446*
447* Multiply by the diagonal block if non-unit.
448*
449 IF( nounit ) THEN
450 d11 = a( k-1, k-1 )
451 d22 = a( k, k )
452 d12 = a( k-1, k )
453 d21 = d12
454 DO 80 j = 1, nrhs
455 t1 = b( k-1, j )
456 t2 = b( k, j )
457 b( k-1, j ) = d11*t1 + d12*t2
458 b( k, j ) = d21*t1 + d22*t2
459 80 CONTINUE
460 END IF
461 k = k - 2
462 END IF
463 GO TO 70
464 90 CONTINUE
465*
466* Form B := L'*B
467* where L = P(1)*inv(L(1))* ... *P(m)*inv(L(m))
468* and L' = inv(L'(m))*P(m)* ... *inv(L'(1))*P(1)
469*
470 ELSE
471*
472* Loop forward applying the L-transformations.
473*
474 k = 1
475 100 CONTINUE
476 IF( k.GT.n )
477 \$ GO TO 120
478*
479* 1 x 1 pivot block
480*
481 IF( ipiv( k ).GT.0 ) THEN
482 IF( k.LT.n ) THEN
483*
484* Interchange if P(K) != I.
485*
486 kp = ipiv( k )
487 IF( kp.NE.k )
488 \$ CALL zswap( nrhs, b( k, 1 ), ldb, b( kp, 1 ), ldb )
489*
490* Apply the transformation
491*
492 CALL zgemv( 'Transpose', n-k, nrhs, cone, b( k+1, 1 ),
493 \$ ldb, a( k+1, k ), 1, cone, b( k, 1 ), ldb )
494 END IF
495 IF( nounit )
496 \$ CALL zscal( nrhs, a( k, k ), b( k, 1 ), ldb )
497 k = k + 1
498*
499* 2 x 2 pivot block.
500*
501 ELSE
502 IF( k.LT.n-1 ) THEN
503*
504* Interchange if P(K) != I.
505*
506 kp = abs( ipiv( k ) )
507 IF( kp.NE.k+1 )
508 \$ CALL zswap( nrhs, b( k+1, 1 ), ldb, b( kp, 1 ),
509 \$ ldb )
510*
511* Apply the transformation
512*
513 CALL zgemv( 'Transpose', n-k-1, nrhs, cone,
514 \$ b( k+2, 1 ), ldb, a( k+2, k+1 ), 1, cone,
515 \$ b( k+1, 1 ), ldb )
516 CALL zgemv( 'Transpose', n-k-1, nrhs, cone,
517 \$ b( k+2, 1 ), ldb, a( k+2, k ), 1, cone,
518 \$ b( k, 1 ), ldb )
519 END IF
520*
521* Multiply by the diagonal block if non-unit.
522*
523 IF( nounit ) THEN
524 d11 = a( k, k )
525 d22 = a( k+1, k+1 )
526 d21 = a( k+1, k )
527 d12 = d21
528 DO 110 j = 1, nrhs
529 t1 = b( k, j )
530 t2 = b( k+1, j )
531 b( k, j ) = d11*t1 + d12*t2
532 b( k+1, j ) = d21*t1 + d22*t2
533 110 CONTINUE
534 END IF
535 k = k + 2
536 END IF
537 GO TO 100
538 120 CONTINUE
539 END IF
540 END IF
541 RETURN
542*
543* End of ZLAVSY
544*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
subroutine zgemv(trans, m, n, alpha, a, lda, x, incx, beta, y, incy)
ZGEMV
Definition zgemv.f:160
subroutine zgeru(m, n, alpha, x, incx, y, incy, a, lda)
ZGERU
Definition zgeru.f:130
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
subroutine zscal(n, za, zx, incx)
ZSCAL
Definition zscal.f:78
subroutine zswap(n, zx, incx, zy, incy)
ZSWAP
Definition zswap.f:81
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