LAPACK  3.6.0 LAPACK: Linear Algebra PACKage
complex16
Collaboration diagram for complex16:


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## Functions

subroutine zgbsv (N, KL, KU, NRHS, AB, LDAB, IPIV, B, LDB, INFO)
ZGBSV computes the solution to system of linear equations A * X = B for GB matrices (simple driver) More...

subroutine zgbsvx (FACT, TRANS, N, KL, KU, NRHS, AB, LDAB, AFB, LDAFB, IPIV, EQUED, R, C, B, LDB, X, LDX, RCOND, FERR, BERR, WORK, RWORK, INFO)
ZGBSVX computes the solution to system of linear equations A * X = B for GB matrices More...

subroutine zgbsvxx (FACT, TRANS, N, KL, KU, NRHS, AB, LDAB, AFB, LDAFB, IPIV, EQUED, R, C, B, LDB, X, LDX, RCOND, RPVGRW, BERR, N_ERR_BNDS, ERR_BNDS_NORM, ERR_BNDS_COMP, NPARAMS, PARAMS, WORK, RWORK, INFO)
ZGBSVXX computes the solution to system of linear equations A * X = B for GB matrices More...

## Detailed Description

This is the group of complex16 solve driver functions for GB matrices

## Function Documentation

 subroutine zgbsv ( integer N, integer KL, integer KU, integer NRHS, complex*16, dimension( ldab, * ) AB, integer LDAB, integer, dimension( * ) IPIV, complex*16, dimension( ldb, * ) B, integer LDB, integer INFO )

ZGBSV computes the solution to system of linear equations A * X = B for GB matrices (simple driver)

Purpose:
``` ZGBSV computes the solution to a complex system of linear equations
A * X = B, where A is a band matrix of order N with KL subdiagonals
and KU superdiagonals, and X and B are N-by-NRHS matrices.

The LU decomposition with partial pivoting and row interchanges is
used to factor A as A = L * U, where L is a product of permutation
and unit lower triangular matrices with KL subdiagonals, and U is
upper triangular with KL+KU superdiagonals.  The factored form of A
is then used to solve the system of equations A * X = B.```
Parameters
 [in] N ``` N is INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0.``` [in] KL ``` KL is INTEGER The number of subdiagonals within the band of A. KL >= 0.``` [in] KU ``` KU is INTEGER The number of superdiagonals within the band of A. KU >= 0.``` [in] NRHS ``` NRHS is INTEGER The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0.``` [in,out] AB ``` AB is COMPLEX*16 array, dimension (LDAB,N) On entry, the matrix A in band storage, in rows KL+1 to 2*KL+KU+1; rows 1 to KL of the array need not be set. The j-th column of A is stored in the j-th column of the array AB as follows: AB(KL+KU+1+i-j,j) = A(i,j) for max(1,j-KU)<=i<=min(N,j+KL) On exit, details of the factorization: U is stored as an upper triangular band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and the multipliers used during the factorization are stored in rows KL+KU+2 to 2*KL+KU+1. See below for further details.``` [in] LDAB ``` LDAB is INTEGER The leading dimension of the array AB. LDAB >= 2*KL+KU+1.``` [out] IPIV ``` IPIV is INTEGER array, dimension (N) The pivot indices that define the permutation matrix P; row i of the matrix was interchanged with row IPIV(i).``` [in,out] B ``` B is COMPLEX*16 array, dimension (LDB,NRHS) On entry, the N-by-NRHS right hand side matrix B. On exit, if INFO = 0, the N-by-NRHS solution matrix X.``` [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 = -i, the i-th argument had an illegal value > 0: if INFO = i, U(i,i) is exactly zero. The factorization has been completed, but the factor U is exactly singular, and the solution has not been computed.```
Date
November 2011
Further Details:
```  The band storage scheme is illustrated by the following example, when
M = N = 6, KL = 2, KU = 1:

On entry:                       On exit:

*    *    *    +    +    +       *    *    *   u14  u25  u36
*    *    +    +    +    +       *    *   u13  u24  u35  u46
*   a12  a23  a34  a45  a56      *   u12  u23  u34  u45  u56
a11  a22  a33  a44  a55  a66     u11  u22  u33  u44  u55  u66
a21  a32  a43  a54  a65   *      m21  m32  m43  m54  m65   *
a31  a42  a53  a64   *    *      m31  m42  m53  m64   *    *

Array elements marked * are not used by the routine; elements marked
+ need not be set on entry, but are required by the routine to store
elements of U because of fill-in resulting from the row interchanges.```

Definition at line 164 of file zgbsv.f.

164 *
165 * -- LAPACK driver routine (version 3.4.0) --
166 * -- LAPACK is a software package provided by Univ. of Tennessee, --
167 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
168 * November 2011
169 *
170 * .. Scalar Arguments ..
171  INTEGER info, kl, ku, ldab, ldb, n, nrhs
172 * ..
173 * .. Array Arguments ..
174  INTEGER ipiv( * )
175  COMPLEX*16 ab( ldab, * ), b( ldb, * )
176 * ..
177 *
178 * =====================================================================
179 *
180 * .. External Subroutines ..
181  EXTERNAL xerbla, zgbtrf, zgbtrs
182 * ..
183 * .. Intrinsic Functions ..
184  INTRINSIC max
185 * ..
186 * .. Executable Statements ..
187 *
188 * Test the input parameters.
189 *
190  info = 0
191  IF( n.LT.0 ) THEN
192  info = -1
193  ELSE IF( kl.LT.0 ) THEN
194  info = -2
195  ELSE IF( ku.LT.0 ) THEN
196  info = -3
197  ELSE IF( nrhs.LT.0 ) THEN
198  info = -4
199  ELSE IF( ldab.LT.2*kl+ku+1 ) THEN
200  info = -6
201  ELSE IF( ldb.LT.max( n, 1 ) ) THEN
202  info = -9
203  END IF
204  IF( info.NE.0 ) THEN
205  CALL xerbla( 'ZGBSV ', -info )
206  RETURN
207  END IF
208 *
209 * Compute the LU factorization of the band matrix A.
210 *
211  CALL zgbtrf( n, n, kl, ku, ab, ldab, ipiv, info )
212  IF( info.EQ.0 ) THEN
213 *
214 * Solve the system A*X = B, overwriting B with X.
215 *
216  CALL zgbtrs( 'No transpose', n, kl, ku, nrhs, ab, ldab, ipiv,
217  \$ b, ldb, info )
218  END IF
219  RETURN
220 *
221 * End of ZGBSV
222 *
subroutine zgbtrf(M, N, KL, KU, AB, LDAB, IPIV, INFO)
ZGBTRF
Definition: zgbtrf.f:146
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine zgbtrs(TRANS, N, KL, KU, NRHS, AB, LDAB, IPIV, B, LDB, INFO)
ZGBTRS
Definition: zgbtrs.f:140

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 subroutine zgbsvx ( character FACT, character TRANS, integer N, integer KL, integer KU, integer NRHS, complex*16, dimension( ldab, * ) AB, integer LDAB, complex*16, dimension( ldafb, * ) AFB, integer LDAFB, integer, dimension( * ) IPIV, character EQUED, double precision, dimension( * ) R, double precision, dimension( * ) C, complex*16, dimension( ldb, * ) B, integer LDB, complex*16, dimension( ldx, * ) X, integer LDX, double precision RCOND, double precision, dimension( * ) FERR, double precision, dimension( * ) BERR, complex*16, dimension( * ) WORK, double precision, dimension( * ) RWORK, integer INFO )

ZGBSVX computes the solution to system of linear equations A * X = B for GB matrices

Purpose:
``` ZGBSVX uses the LU factorization to compute the solution to a complex
system of linear equations A * X = B, A**T * X = B, or A**H * X = B,
where A is a band matrix of order N with KL subdiagonals and KU
superdiagonals, and X and B are N-by-NRHS matrices.

Error bounds on the solution and a condition estimate are also
provided.```
Description:
``` The following steps are performed by this subroutine:

1. If FACT = 'E', real scaling factors are computed to equilibrate
the system:
TRANS = 'N':  diag(R)*A*diag(C)     *inv(diag(C))*X = diag(R)*B
TRANS = 'T': (diag(R)*A*diag(C))**T *inv(diag(R))*X = diag(C)*B
TRANS = 'C': (diag(R)*A*diag(C))**H *inv(diag(R))*X = diag(C)*B
Whether or not the system will be equilibrated depends on the
scaling of the matrix A, but if equilibration is used, A is
overwritten by diag(R)*A*diag(C) and B by diag(R)*B (if TRANS='N')
or diag(C)*B (if TRANS = 'T' or 'C').

2. If FACT = 'N' or 'E', the LU decomposition is used to factor the
matrix A (after equilibration if FACT = 'E') as
A = L * U,
where L is a product of permutation and unit lower triangular
matrices with KL subdiagonals, and U is upper triangular with
KL+KU superdiagonals.

3. If some U(i,i)=0, so that U is exactly singular, then the routine
returns with INFO = i. Otherwise, the factored form of A is used
to estimate the condition number of the matrix A.  If the
reciprocal of the condition number is less than machine precision,
INFO = N+1 is returned as a warning, but the routine still goes on
to solve for X and compute error bounds as described below.

4. The system of equations is solved for X using the factored form
of A.

5. Iterative refinement is applied to improve the computed solution
matrix and calculate error bounds and backward error estimates
for it.

6. If equilibration was used, the matrix X is premultiplied by
diag(C) (if TRANS = 'N') or diag(R) (if TRANS = 'T' or 'C') so
that it solves the original system before equilibration.```
Parameters
 [in] FACT ``` FACT is CHARACTER*1 Specifies whether or not the factored form of the matrix A is supplied on entry, and if not, whether the matrix A should be equilibrated before it is factored. = 'F': On entry, AFB and IPIV contain the factored form of A. If EQUED is not 'N', the matrix A has been equilibrated with scaling factors given by R and C. AB, AFB, and IPIV are not modified. = 'N': The matrix A will be copied to AFB and factored. = 'E': The matrix A will be equilibrated if necessary, then copied to AFB and factored.``` [in] TRANS ``` TRANS is CHARACTER*1 Specifies the form of the system of equations. = 'N': A * X = B (No transpose) = 'T': A**T * X = B (Transpose) = 'C': A**H * X = B (Conjugate transpose)``` [in] N ``` N is INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0.``` [in] KL ``` KL is INTEGER The number of subdiagonals within the band of A. KL >= 0.``` [in] KU ``` KU is INTEGER The number of superdiagonals within the band of A. KU >= 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] AB ``` AB is COMPLEX*16 array, dimension (LDAB,N) On entry, the matrix A in band storage, in rows 1 to KL+KU+1. The j-th column of A is stored in the j-th column of the array AB as follows: AB(KU+1+i-j,j) = A(i,j) for max(1,j-KU)<=i<=min(N,j+kl) If FACT = 'F' and EQUED is not 'N', then A must have been equilibrated by the scaling factors in R and/or C. AB is not modified if FACT = 'F' or 'N', or if FACT = 'E' and EQUED = 'N' on exit. On exit, if EQUED .ne. 'N', A is scaled as follows: EQUED = 'R': A := diag(R) * A EQUED = 'C': A := A * diag(C) EQUED = 'B': A := diag(R) * A * diag(C).``` [in] LDAB ``` LDAB is INTEGER The leading dimension of the array AB. LDAB >= KL+KU+1.``` [in,out] AFB ``` AFB is COMPLEX*16 array, dimension (LDAFB,N) If FACT = 'F', then AFB is an input argument and on entry contains details of the LU factorization of the band matrix A, as computed by ZGBTRF. U is stored as an upper triangular band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and the multipliers used during the factorization are stored in rows KL+KU+2 to 2*KL+KU+1. If EQUED .ne. 'N', then AFB is the factored form of the equilibrated matrix A. If FACT = 'N', then AFB is an output argument and on exit returns details of the LU factorization of A. If FACT = 'E', then AFB is an output argument and on exit returns details of the LU factorization of the equilibrated matrix A (see the description of AB for the form of the equilibrated matrix).``` [in] LDAFB ``` LDAFB is INTEGER The leading dimension of the array AFB. LDAFB >= 2*KL+KU+1.``` [in,out] IPIV ``` IPIV is INTEGER array, dimension (N) If FACT = 'F', then IPIV is an input argument and on entry contains the pivot indices from the factorization A = L*U as computed by ZGBTRF; row i of the matrix was interchanged with row IPIV(i). If FACT = 'N', then IPIV is an output argument and on exit contains the pivot indices from the factorization A = L*U of the original matrix A. If FACT = 'E', then IPIV is an output argument and on exit contains the pivot indices from the factorization A = L*U of the equilibrated matrix A.``` [in,out] EQUED ``` EQUED is CHARACTER*1 Specifies the form of equilibration that was done. = 'N': No equilibration (always true if FACT = 'N'). = 'R': Row equilibration, i.e., A has been premultiplied by diag(R). = 'C': Column equilibration, i.e., A has been postmultiplied by diag(C). = 'B': Both row and column equilibration, i.e., A has been replaced by diag(R) * A * diag(C). EQUED is an input argument if FACT = 'F'; otherwise, it is an output argument.``` [in,out] R ``` R is DOUBLE PRECISION array, dimension (N) The row scale factors for A. If EQUED = 'R' or 'B', A is multiplied on the left by diag(R); if EQUED = 'N' or 'C', R is not accessed. R is an input argument if FACT = 'F'; otherwise, R is an output argument. If FACT = 'F' and EQUED = 'R' or 'B', each element of R must be positive.``` [in,out] C ``` C is DOUBLE PRECISION array, dimension (N) The column scale factors for A. If EQUED = 'C' or 'B', A is multiplied on the right by diag(C); if EQUED = 'N' or 'R', C is not accessed. C is an input argument if FACT = 'F'; otherwise, C is an output argument. If FACT = 'F' and EQUED = 'C' or 'B', each element of C must be positive.``` [in,out] B ``` B is COMPLEX*16 array, dimension (LDB,NRHS) On entry, the right hand side matrix B. On exit, if EQUED = 'N', B is not modified; if TRANS = 'N' and EQUED = 'R' or 'B', B is overwritten by diag(R)*B; if TRANS = 'T' or 'C' and EQUED = 'C' or 'B', B is overwritten by diag(C)*B.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N).``` [out] X ``` X is COMPLEX*16 array, dimension (LDX,NRHS) If INFO = 0 or INFO = N+1, the N-by-NRHS solution matrix X to the original system of equations. Note that A and B are modified on exit if EQUED .ne. 'N', and the solution to the equilibrated system is inv(diag(C))*X if TRANS = 'N' and EQUED = 'C' or 'B', or inv(diag(R))*X if TRANS = 'T' or 'C' and EQUED = 'R' or 'B'.``` [in] LDX ``` LDX is INTEGER The leading dimension of the array X. LDX >= max(1,N).``` [out] RCOND ``` RCOND is DOUBLE PRECISION The estimate of the reciprocal condition number of the matrix A after equilibration (if done). If RCOND is less than the machine precision (in particular, if RCOND = 0), the matrix is singular to working precision. This condition is indicated by a return code of INFO > 0.``` [out] FERR ``` FERR is DOUBLE PRECISION array, dimension (NRHS) The estimated forward error bound for each solution vector X(j) (the j-th column of the solution matrix X). If XTRUE is the true solution corresponding to X(j), FERR(j) is an estimated upper bound for the magnitude of the largest element in (X(j) - XTRUE) divided by the magnitude of the largest element in X(j). The estimate is as reliable as the estimate for RCOND, and is almost always a slight overestimate of the true error.``` [out] BERR ``` BERR is DOUBLE PRECISION array, dimension (NRHS) The componentwise relative backward error of each solution vector X(j) (i.e., the smallest relative change in any element of A or B that makes X(j) an exact solution).``` [out] WORK ` WORK is COMPLEX*16 array, dimension (2*N)` [out] RWORK ``` RWORK is DOUBLE PRECISION array, dimension (N) On exit, RWORK(1) contains the reciprocal pivot growth factor norm(A)/norm(U). The "max absolute element" norm is used. If RWORK(1) is much less than 1, then the stability of the LU factorization of the (equilibrated) matrix A could be poor. This also means that the solution X, condition estimator RCOND, and forward error bound FERR could be unreliable. If factorization fails with 0 0: if INFO = i, and i is <= N: U(i,i) is exactly zero. The factorization has been completed, but the factor U is exactly singular, so the solution and error bounds could not be computed. RCOND = 0 is returned. = N+1: U is nonsingular, but RCOND is less than machine precision, meaning that the matrix is singular to working precision. Nevertheless, the solution and error bounds are computed because there are a number of situations where the computed solution can be more accurate than the value of RCOND would suggest.```
Date
April 2012

Definition at line 372 of file zgbsvx.f.

372 *
373 * -- LAPACK driver routine (version 3.4.1) --
374 * -- LAPACK is a software package provided by Univ. of Tennessee, --
375 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
376 * April 2012
377 *
378 * .. Scalar Arguments ..
379  CHARACTER equed, fact, trans
380  INTEGER info, kl, ku, ldab, ldafb, ldb, ldx, n, nrhs
381  DOUBLE PRECISION rcond
382 * ..
383 * .. Array Arguments ..
384  INTEGER ipiv( * )
385  DOUBLE PRECISION berr( * ), c( * ), ferr( * ), r( * ),
386  \$ rwork( * )
387  COMPLEX*16 ab( ldab, * ), afb( ldafb, * ), b( ldb, * ),
388  \$ work( * ), x( ldx, * )
389 * ..
390 *
391 * =====================================================================
392 * Moved setting of INFO = N+1 so INFO does not subsequently get
393 * overwritten. Sven, 17 Mar 05.
394 * =====================================================================
395 *
396 * .. Parameters ..
397  DOUBLE PRECISION zero, one
398  parameter( zero = 0.0d+0, one = 1.0d+0 )
399 * ..
400 * .. Local Scalars ..
401  LOGICAL colequ, equil, nofact, notran, rowequ
402  CHARACTER norm
403  INTEGER i, infequ, j, j1, j2
404  DOUBLE PRECISION amax, anorm, bignum, colcnd, rcmax, rcmin,
405  \$ rowcnd, rpvgrw, smlnum
406 * ..
407 * .. External Functions ..
408  LOGICAL lsame
409  DOUBLE PRECISION dlamch, zlangb, zlantb
410  EXTERNAL lsame, dlamch, zlangb, zlantb
411 * ..
412 * .. External Subroutines ..
413  EXTERNAL xerbla, zcopy, zgbcon, zgbequ, zgbrfs, zgbtrf,
414  \$ zgbtrs, zlacpy, zlaqgb
415 * ..
416 * .. Intrinsic Functions ..
417  INTRINSIC abs, max, min
418 * ..
419 * .. Executable Statements ..
420 *
421  info = 0
422  nofact = lsame( fact, 'N' )
423  equil = lsame( fact, 'E' )
424  notran = lsame( trans, 'N' )
425  IF( nofact .OR. equil ) THEN
426  equed = 'N'
427  rowequ = .false.
428  colequ = .false.
429  ELSE
430  rowequ = lsame( equed, 'R' ) .OR. lsame( equed, 'B' )
431  colequ = lsame( equed, 'C' ) .OR. lsame( equed, 'B' )
432  smlnum = dlamch( 'Safe minimum' )
433  bignum = one / smlnum
434  END IF
435 *
436 * Test the input parameters.
437 *
438  IF( .NOT.nofact .AND. .NOT.equil .AND. .NOT.lsame( fact, 'F' ) )
439  \$ THEN
440  info = -1
441  ELSE IF( .NOT.notran .AND. .NOT.lsame( trans, 'T' ) .AND. .NOT.
442  \$ lsame( trans, 'C' ) ) THEN
443  info = -2
444  ELSE IF( n.LT.0 ) THEN
445  info = -3
446  ELSE IF( kl.LT.0 ) THEN
447  info = -4
448  ELSE IF( ku.LT.0 ) THEN
449  info = -5
450  ELSE IF( nrhs.LT.0 ) THEN
451  info = -6
452  ELSE IF( ldab.LT.kl+ku+1 ) THEN
453  info = -8
454  ELSE IF( ldafb.LT.2*kl+ku+1 ) THEN
455  info = -10
456  ELSE IF( lsame( fact, 'F' ) .AND. .NOT.
457  \$ ( rowequ .OR. colequ .OR. lsame( equed, 'N' ) ) ) THEN
458  info = -12
459  ELSE
460  IF( rowequ ) THEN
461  rcmin = bignum
462  rcmax = zero
463  DO 10 j = 1, n
464  rcmin = min( rcmin, r( j ) )
465  rcmax = max( rcmax, r( j ) )
466  10 CONTINUE
467  IF( rcmin.LE.zero ) THEN
468  info = -13
469  ELSE IF( n.GT.0 ) THEN
470  rowcnd = max( rcmin, smlnum ) / min( rcmax, bignum )
471  ELSE
472  rowcnd = one
473  END IF
474  END IF
475  IF( colequ .AND. info.EQ.0 ) THEN
476  rcmin = bignum
477  rcmax = zero
478  DO 20 j = 1, n
479  rcmin = min( rcmin, c( j ) )
480  rcmax = max( rcmax, c( j ) )
481  20 CONTINUE
482  IF( rcmin.LE.zero ) THEN
483  info = -14
484  ELSE IF( n.GT.0 ) THEN
485  colcnd = max( rcmin, smlnum ) / min( rcmax, bignum )
486  ELSE
487  colcnd = one
488  END IF
489  END IF
490  IF( info.EQ.0 ) THEN
491  IF( ldb.LT.max( 1, n ) ) THEN
492  info = -16
493  ELSE IF( ldx.LT.max( 1, n ) ) THEN
494  info = -18
495  END IF
496  END IF
497  END IF
498 *
499  IF( info.NE.0 ) THEN
500  CALL xerbla( 'ZGBSVX', -info )
501  RETURN
502  END IF
503 *
504  IF( equil ) THEN
505 *
506 * Compute row and column scalings to equilibrate the matrix A.
507 *
508  CALL zgbequ( n, n, kl, ku, ab, ldab, r, c, rowcnd, colcnd,
509  \$ amax, infequ )
510  IF( infequ.EQ.0 ) THEN
511 *
512 * Equilibrate the matrix.
513 *
514  CALL zlaqgb( n, n, kl, ku, ab, ldab, r, c, rowcnd, colcnd,
515  \$ amax, equed )
516  rowequ = lsame( equed, 'R' ) .OR. lsame( equed, 'B' )
517  colequ = lsame( equed, 'C' ) .OR. lsame( equed, 'B' )
518  END IF
519  END IF
520 *
521 * Scale the right hand side.
522 *
523  IF( notran ) THEN
524  IF( rowequ ) THEN
525  DO 40 j = 1, nrhs
526  DO 30 i = 1, n
527  b( i, j ) = r( i )*b( i, j )
528  30 CONTINUE
529  40 CONTINUE
530  END IF
531  ELSE IF( colequ ) THEN
532  DO 60 j = 1, nrhs
533  DO 50 i = 1, n
534  b( i, j ) = c( i )*b( i, j )
535  50 CONTINUE
536  60 CONTINUE
537  END IF
538 *
539  IF( nofact .OR. equil ) THEN
540 *
541 * Compute the LU factorization of the band matrix A.
542 *
543  DO 70 j = 1, n
544  j1 = max( j-ku, 1 )
545  j2 = min( j+kl, n )
546  CALL zcopy( j2-j1+1, ab( ku+1-j+j1, j ), 1,
547  \$ afb( kl+ku+1-j+j1, j ), 1 )
548  70 CONTINUE
549 *
550  CALL zgbtrf( n, n, kl, ku, afb, ldafb, ipiv, info )
551 *
552 * Return if INFO is non-zero.
553 *
554  IF( info.GT.0 ) THEN
555 *
556 * Compute the reciprocal pivot growth factor of the
557 * leading rank-deficient INFO columns of A.
558 *
559  anorm = zero
560  DO 90 j = 1, info
561  DO 80 i = max( ku+2-j, 1 ), min( n+ku+1-j, kl+ku+1 )
562  anorm = max( anorm, abs( ab( i, j ) ) )
563  80 CONTINUE
564  90 CONTINUE
565  rpvgrw = zlantb( 'M', 'U', 'N', info, min( info-1, kl+ku ),
566  \$ afb( max( 1, kl+ku+2-info ), 1 ), ldafb,
567  \$ rwork )
568  IF( rpvgrw.EQ.zero ) THEN
569  rpvgrw = one
570  ELSE
571  rpvgrw = anorm / rpvgrw
572  END IF
573  rwork( 1 ) = rpvgrw
574  rcond = zero
575  RETURN
576  END IF
577  END IF
578 *
579 * Compute the norm of the matrix A and the
580 * reciprocal pivot growth factor RPVGRW.
581 *
582  IF( notran ) THEN
583  norm = '1'
584  ELSE
585  norm = 'I'
586  END IF
587  anorm = zlangb( norm, n, kl, ku, ab, ldab, rwork )
588  rpvgrw = zlantb( 'M', 'U', 'N', n, kl+ku, afb, ldafb, rwork )
589  IF( rpvgrw.EQ.zero ) THEN
590  rpvgrw = one
591  ELSE
592  rpvgrw = zlangb( 'M', n, kl, ku, ab, ldab, rwork ) / rpvgrw
593  END IF
594 *
595 * Compute the reciprocal of the condition number of A.
596 *
597  CALL zgbcon( norm, n, kl, ku, afb, ldafb, ipiv, anorm, rcond,
598  \$ work, rwork, info )
599 *
600 * Compute the solution matrix X.
601 *
602  CALL zlacpy( 'Full', n, nrhs, b, ldb, x, ldx )
603  CALL zgbtrs( trans, n, kl, ku, nrhs, afb, ldafb, ipiv, x, ldx,
604  \$ info )
605 *
606 * Use iterative refinement to improve the computed solution and
607 * compute error bounds and backward error estimates for it.
608 *
609  CALL zgbrfs( trans, n, kl, ku, nrhs, ab, ldab, afb, ldafb, ipiv,
610  \$ b, ldb, x, ldx, ferr, berr, work, rwork, info )
611 *
612 * Transform the solution matrix X to a solution of the original
613 * system.
614 *
615  IF( notran ) THEN
616  IF( colequ ) THEN
617  DO 110 j = 1, nrhs
618  DO 100 i = 1, n
619  x( i, j ) = c( i )*x( i, j )
620  100 CONTINUE
621  110 CONTINUE
622  DO 120 j = 1, nrhs
623  ferr( j ) = ferr( j ) / colcnd
624  120 CONTINUE
625  END IF
626  ELSE IF( rowequ ) THEN
627  DO 140 j = 1, nrhs
628  DO 130 i = 1, n
629  x( i, j ) = r( i )*x( i, j )
630  130 CONTINUE
631  140 CONTINUE
632  DO 150 j = 1, nrhs
633  ferr( j ) = ferr( j ) / rowcnd
634  150 CONTINUE
635  END IF
636 *
637 * Set INFO = N+1 if the matrix is singular to working precision.
638 *
639  IF( rcond.LT.dlamch( 'Epsilon' ) )
640  \$ info = n + 1
641 *
642  rwork( 1 ) = rpvgrw
643  RETURN
644 *
645 * End of ZGBSVX
646 *
subroutine zgbtrf(M, N, KL, KU, AB, LDAB, IPIV, INFO)
ZGBTRF
Definition: zgbtrf.f:146
double precision function zlantb(NORM, UPLO, DIAG, N, K, AB, LDAB, WORK)
ZLANTB returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a triangular band matrix.
Definition: zlantb.f:143
subroutine zlacpy(UPLO, M, N, A, LDA, B, LDB)
ZLACPY copies all or part of one two-dimensional array to another.
Definition: zlacpy.f:105
subroutine zcopy(N, ZX, INCX, ZY, INCY)
ZCOPY
Definition: zcopy.f:52
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine zgbtrs(TRANS, N, KL, KU, NRHS, AB, LDAB, IPIV, B, LDB, INFO)
ZGBTRS
Definition: zgbtrs.f:140
subroutine zgbequ(M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND, AMAX, INFO)
ZGBEQU
Definition: zgbequ.f:156
subroutine zgbrfs(TRANS, N, KL, KU, NRHS, AB, LDAB, AFB, LDAFB, IPIV, B, LDB, X, LDX, FERR, BERR, WORK, RWORK, INFO)
ZGBRFS
Definition: zgbrfs.f:208
subroutine zgbcon(NORM, N, KL, KU, AB, LDAB, IPIV, ANORM, RCOND, WORK, RWORK, INFO)
ZGBCON
Definition: zgbcon.f:149
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:65
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55
double precision function zlangb(NORM, N, KL, KU, AB, LDAB, WORK)
ZLANGB returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value ...
Definition: zlangb.f:127
subroutine zlaqgb(M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND, AMAX, EQUED)
ZLAQGB scales a general band matrix, using row and column scaling factors computed by sgbequ...
Definition: zlaqgb.f:162

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 subroutine zgbsvxx ( character FACT, character TRANS, integer N, integer KL, integer KU, integer NRHS, complex*16, dimension( ldab, * ) AB, integer LDAB, complex*16, dimension( ldafb, * ) AFB, integer LDAFB, integer, dimension( * ) IPIV, character EQUED, double precision, dimension( * ) R, double precision, dimension( * ) C, complex*16, dimension( ldb, * ) B, integer LDB, complex*16, dimension( ldx , * ) X, integer LDX, double precision RCOND, double precision RPVGRW, double precision, dimension( * ) BERR, integer N_ERR_BNDS, double precision, dimension( nrhs, * ) ERR_BNDS_NORM, double precision, dimension( nrhs, * ) ERR_BNDS_COMP, integer NPARAMS, double precision, dimension( * ) PARAMS, complex*16, dimension( * ) WORK, double precision, dimension( * ) RWORK, integer INFO )

ZGBSVXX computes the solution to system of linear equations A * X = B for GB matrices

Purpose:
```    ZGBSVXX uses the LU factorization to compute the solution to a
complex*16 system of linear equations  A * X = B,  where A is an
N-by-N matrix and X and B are N-by-NRHS matrices.

If requested, both normwise and maximum componentwise error bounds
are returned. ZGBSVXX will return a solution with a tiny
guaranteed error (O(eps) where eps is the working machine
precision) unless the matrix is very ill-conditioned, in which
case a warning is returned. Relevant condition numbers also are
calculated and returned.

ZGBSVXX accepts user-provided factorizations and equilibration
factors; see the definitions of the FACT and EQUED options.
Solving with refinement and using a factorization from a previous
ZGBSVXX call will also produce a solution with either O(eps)
errors or warnings, but we cannot make that claim for general
user-provided factorizations and equilibration factors if they
differ from what ZGBSVXX would itself produce.```
Description:
```    The following steps are performed:

1. If FACT = 'E', double precision scaling factors are computed to equilibrate
the system:

TRANS = 'N':  diag(R)*A*diag(C)     *inv(diag(C))*X = diag(R)*B
TRANS = 'T': (diag(R)*A*diag(C))**T *inv(diag(R))*X = diag(C)*B
TRANS = 'C': (diag(R)*A*diag(C))**H *inv(diag(R))*X = diag(C)*B

Whether or not the system will be equilibrated depends on the
scaling of the matrix A, but if equilibration is used, A is
overwritten by diag(R)*A*diag(C) and B by diag(R)*B (if TRANS='N')
or diag(C)*B (if TRANS = 'T' or 'C').

2. If FACT = 'N' or 'E', the LU decomposition is used to factor
the matrix A (after equilibration if FACT = 'E') as

A = P * L * U,

where P is a permutation matrix, L is a unit lower triangular
matrix, and U is upper triangular.

3. If some U(i,i)=0, so that U is exactly singular, then the
routine returns with INFO = i. Otherwise, the factored form of A
is used to estimate the condition number of the matrix A (see
argument RCOND). If the reciprocal of the condition number is less
than machine precision, the routine still goes on to solve for X
and compute error bounds as described below.

4. The system of equations is solved for X using the factored form
of A.

5. By default (unless PARAMS(LA_LINRX_ITREF_I) is set to zero),
the routine will use iterative refinement to try to get a small
error and error bounds.  Refinement calculates the residual to at
least twice the working precision.

6. If equilibration was used, the matrix X is premultiplied by
diag(C) (if TRANS = 'N') or diag(R) (if TRANS = 'T' or 'C') so
that it solves the original system before equilibration.```
```     Some optional parameters are bundled in the PARAMS array.  These
settings determine how refinement is performed, but often the
defaults are acceptable.  If the defaults are acceptable, users
can pass NPARAMS = 0 which prevents the source code from accessing
the PARAMS argument.```
Parameters
 [in] FACT ``` FACT is CHARACTER*1 Specifies whether or not the factored form of the matrix A is supplied on entry, and if not, whether the matrix A should be equilibrated before it is factored. = 'F': On entry, AF and IPIV contain the factored form of A. If EQUED is not 'N', the matrix A has been equilibrated with scaling factors given by R and C. A, AF, and IPIV are not modified. = 'N': The matrix A will be copied to AF and factored. = 'E': The matrix A will be equilibrated if necessary, then copied to AF and factored.``` [in] TRANS ``` TRANS is CHARACTER*1 Specifies the form of the system of equations: = 'N': A * X = B (No transpose) = 'T': A**T * X = B (Transpose) = 'C': A**H * X = B (Conjugate Transpose = Transpose)``` [in] N ``` N is INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0.``` [in] KL ``` KL is INTEGER The number of subdiagonals within the band of A. KL >= 0.``` [in] KU ``` KU is INTEGER The number of superdiagonals within the band of A. KU >= 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] AB ``` AB is COMPLEX*16 array, dimension (LDAB,N) On entry, the matrix A in band storage, in rows 1 to KL+KU+1. The j-th column of A is stored in the j-th column of the array AB as follows: AB(KU+1+i-j,j) = A(i,j) for max(1,j-KU)<=i<=min(N,j+kl) If FACT = 'F' and EQUED is not 'N', then AB must have been equilibrated by the scaling factors in R and/or C. AB is not modified if FACT = 'F' or 'N', or if FACT = 'E' and EQUED = 'N' on exit. On exit, if EQUED .ne. 'N', A is scaled as follows: EQUED = 'R': A := diag(R) * A EQUED = 'C': A := A * diag(C) EQUED = 'B': A := diag(R) * A * diag(C).``` [in] LDAB ``` LDAB is INTEGER The leading dimension of the array AB. LDAB >= KL+KU+1.``` [in,out] AFB ``` AFB is COMPLEX*16 array, dimension (LDAFB,N) If FACT = 'F', then AFB is an input argument and on entry contains details of the LU factorization of the band matrix A, as computed by ZGBTRF. U is stored as an upper triangular band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and the multipliers used during the factorization are stored in rows KL+KU+2 to 2*KL+KU+1. If EQUED .ne. 'N', then AFB is the factored form of the equilibrated matrix A. If FACT = 'N', then AF is an output argument and on exit returns the factors L and U from the factorization A = P*L*U of the original matrix A. If FACT = 'E', then AF is an output argument and on exit returns the factors L and U from the factorization A = P*L*U of the equilibrated matrix A (see the description of A for the form of the equilibrated matrix).``` [in] LDAFB ``` LDAFB is INTEGER The leading dimension of the array AFB. LDAFB >= 2*KL+KU+1.``` [in,out] IPIV ``` IPIV is INTEGER array, dimension (N) If FACT = 'F', then IPIV is an input argument and on entry contains the pivot indices from the factorization A = P*L*U as computed by DGETRF; row i of the matrix was interchanged with row IPIV(i). If FACT = 'N', then IPIV is an output argument and on exit contains the pivot indices from the factorization A = P*L*U of the original matrix A. If FACT = 'E', then IPIV is an output argument and on exit contains the pivot indices from the factorization A = P*L*U of the equilibrated matrix A.``` [in,out] EQUED ``` EQUED is CHARACTER*1 Specifies the form of equilibration that was done. = 'N': No equilibration (always true if FACT = 'N'). = 'R': Row equilibration, i.e., A has been premultiplied by diag(R). = 'C': Column equilibration, i.e., A has been postmultiplied by diag(C). = 'B': Both row and column equilibration, i.e., A has been replaced by diag(R) * A * diag(C). EQUED is an input argument if FACT = 'F'; otherwise, it is an output argument.``` [in,out] R ``` R is DOUBLE PRECISION array, dimension (N) The row scale factors for A. If EQUED = 'R' or 'B', A is multiplied on the left by diag(R); if EQUED = 'N' or 'C', R is not accessed. R is an input argument if FACT = 'F'; otherwise, R is an output argument. If FACT = 'F' and EQUED = 'R' or 'B', each element of R must be positive. If R is output, each element of R is a power of the radix. If R is input, each element of R should be a power of the radix to ensure a reliable solution and error estimates. Scaling by powers of the radix does not cause rounding errors unless the result underflows or overflows. Rounding errors during scaling lead to refining with a matrix that is not equivalent to the input matrix, producing error estimates that may not be reliable.``` [in,out] C ``` C is DOUBLE PRECISION array, dimension (N) The column scale factors for A. If EQUED = 'C' or 'B', A is multiplied on the right by diag(C); if EQUED = 'N' or 'R', C is not accessed. C is an input argument if FACT = 'F'; otherwise, C is an output argument. If FACT = 'F' and EQUED = 'C' or 'B', each element of C must be positive. If C is output, each element of C is a power of the radix. If C is input, each element of C should be a power of the radix to ensure a reliable solution and error estimates. Scaling by powers of the radix does not cause rounding errors unless the result underflows or overflows. Rounding errors during scaling lead to refining with a matrix that is not equivalent to the input matrix, producing error estimates that may not be reliable.``` [in,out] B ``` B is COMPLEX*16 array, dimension (LDB,NRHS) On entry, the N-by-NRHS right hand side matrix B. On exit, if EQUED = 'N', B is not modified; if TRANS = 'N' and EQUED = 'R' or 'B', B is overwritten by diag(R)*B; if TRANS = 'T' or 'C' and EQUED = 'C' or 'B', B is overwritten by diag(C)*B.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N).``` [out] X ``` X is COMPLEX*16 array, dimension (LDX,NRHS) If INFO = 0, the N-by-NRHS solution matrix X to the original system of equations. Note that A and B are modified on exit if EQUED .ne. 'N', and the solution to the equilibrated system is inv(diag(C))*X if TRANS = 'N' and EQUED = 'C' or 'B', or inv(diag(R))*X if TRANS = 'T' or 'C' and EQUED = 'R' or 'B'.``` [in] LDX ``` LDX is INTEGER The leading dimension of the array X. LDX >= max(1,N).``` [out] RCOND ``` RCOND is DOUBLE PRECISION Reciprocal scaled condition number. This is an estimate of the reciprocal Skeel condition number of the matrix A after equilibration (if done). If this is less than the machine precision (in particular, if it is zero), the matrix is singular to working precision. Note that the error may still be small even if this number is very small and the matrix appears ill- conditioned.``` [out] RPVGRW ``` RPVGRW is DOUBLE PRECISION Reciprocal pivot growth. On exit, this contains the reciprocal pivot growth factor norm(A)/norm(U). The "max absolute element" norm is used. If this is much less than 1, then the stability of the LU factorization of the (equilibrated) matrix A could be poor. This also means that the solution X, estimated condition numbers, and error bounds could be unreliable. If factorization fails with 0 0 and <= N: U(INFO,INFO) is exactly zero. The factorization has been completed, but the factor U is exactly singular, so the solution and error bounds could not be computed. RCOND = 0 is returned. = N+J: The solution corresponding to the Jth right-hand side is not guaranteed. The solutions corresponding to other right- hand sides K with K > J may not be guaranteed as well, but only the first such right-hand side is reported. If a small componentwise error is not requested (PARAMS(3) = 0.0) then the Jth right-hand side is the first with a normwise error bound that is not guaranteed (the smallest J such that ERR_BNDS_NORM(J,1) = 0.0). By default (PARAMS(3) = 1.0) the Jth right-hand side is the first with either a normwise or componentwise error bound that is not guaranteed (the smallest J such that either ERR_BNDS_NORM(J,1) = 0.0 or ERR_BNDS_COMP(J,1) = 0.0). See the definition of ERR_BNDS_NORM(:,1) and ERR_BNDS_COMP(:,1). To get information about all of the right-hand sides check ERR_BNDS_NORM or ERR_BNDS_COMP.```
Date
April 2012

Definition at line 562 of file zgbsvxx.f.

562 *
563 * -- LAPACK driver routine (version 3.4.1) --
564 * -- LAPACK is a software package provided by Univ. of Tennessee, --
565 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
566 * April 2012
567 *
568 * .. Scalar Arguments ..
569  CHARACTER equed, fact, trans
570  INTEGER info, ldab, ldafb, ldb, ldx, n, nrhs, nparams,
571  \$ n_err_bnds
572  DOUBLE PRECISION rcond, rpvgrw
573 * ..
574 * .. Array Arguments ..
575  INTEGER ipiv( * )
576  COMPLEX*16 ab( ldab, * ), afb( ldafb, * ), b( ldb, * ),
577  \$ x( ldx , * ),work( * )
578  DOUBLE PRECISION r( * ), c( * ), params( * ), berr( * ),
579  \$ err_bnds_norm( nrhs, * ),
580  \$ err_bnds_comp( nrhs, * ), rwork( * )
581 * ..
582 *
583 * ==================================================================
584 *
585 * .. Parameters ..
586  DOUBLE PRECISION zero, one
587  parameter( zero = 0.0d+0, one = 1.0d+0 )
588  INTEGER final_nrm_err_i, final_cmp_err_i, berr_i
589  INTEGER rcond_i, nrm_rcond_i, nrm_err_i, cmp_rcond_i
590  INTEGER cmp_err_i, piv_growth_i
591  parameter( final_nrm_err_i = 1, final_cmp_err_i = 2,
592  \$ berr_i = 3 )
593  parameter( rcond_i = 4, nrm_rcond_i = 5, nrm_err_i = 6 )
594  parameter( cmp_rcond_i = 7, cmp_err_i = 8,
595  \$ piv_growth_i = 9 )
596 * ..
597 * .. Local Scalars ..
598  LOGICAL colequ, equil, nofact, notran, rowequ
599  INTEGER infequ, i, j, kl, ku
600  DOUBLE PRECISION amax, bignum, colcnd, rcmax, rcmin,
601  \$ rowcnd, smlnum
602 * ..
603 * .. External Functions ..
604  EXTERNAL lsame, dlamch, zla_gbrpvgrw
605  LOGICAL lsame
606  DOUBLE PRECISION dlamch, zla_gbrpvgrw
607 * ..
608 * .. External Subroutines ..
609  EXTERNAL zgbequb, zgbtrf, zgbtrs, zlacpy, zlaqgb,
611 * ..
612 * .. Intrinsic Functions ..
613  INTRINSIC max, min
614 * ..
615 * .. Executable Statements ..
616 *
617  info = 0
618  nofact = lsame( fact, 'N' )
619  equil = lsame( fact, 'E' )
620  notran = lsame( trans, 'N' )
621  smlnum = dlamch( 'Safe minimum' )
622  bignum = one / smlnum
623  IF( nofact .OR. equil ) THEN
624  equed = 'N'
625  rowequ = .false.
626  colequ = .false.
627  ELSE
628  rowequ = lsame( equed, 'R' ) .OR. lsame( equed, 'B' )
629  colequ = lsame( equed, 'C' ) .OR. lsame( equed, 'B' )
630  END IF
631 *
632 * Default is failure. If an input parameter is wrong or
633 * factorization fails, make everything look horrible. Only the
634 * pivot growth is set here, the rest is initialized in ZGBRFSX.
635 *
636  rpvgrw = zero
637 *
638 * Test the input parameters. PARAMS is not tested until DGERFSX.
639 *
640  IF( .NOT.nofact .AND. .NOT.equil .AND. .NOT.
641  \$ lsame( fact, 'F' ) ) THEN
642  info = -1
643  ELSE IF( .NOT.notran .AND. .NOT.lsame( trans, 'T' ) .AND. .NOT.
644  \$ lsame( trans, 'C' ) ) THEN
645  info = -2
646  ELSE IF( n.LT.0 ) THEN
647  info = -3
648  ELSE IF( kl.LT.0 ) THEN
649  info = -4
650  ELSE IF( ku.LT.0 ) THEN
651  info = -5
652  ELSE IF( nrhs.LT.0 ) THEN
653  info = -6
654  ELSE IF( ldab.LT.kl+ku+1 ) THEN
655  info = -8
656  ELSE IF( ldafb.LT.2*kl+ku+1 ) THEN
657  info = -10
658  ELSE IF( lsame( fact, 'F' ) .AND. .NOT.
659  \$ ( rowequ .OR. colequ .OR. lsame( equed, 'N' ) ) ) THEN
660  info = -12
661  ELSE
662  IF( rowequ ) THEN
663  rcmin = bignum
664  rcmax = zero
665  DO 10 j = 1, n
666  rcmin = min( rcmin, r( j ) )
667  rcmax = max( rcmax, r( j ) )
668  10 CONTINUE
669  IF( rcmin.LE.zero ) THEN
670  info = -13
671  ELSE IF( n.GT.0 ) THEN
672  rowcnd = max( rcmin, smlnum ) / min( rcmax, bignum )
673  ELSE
674  rowcnd = one
675  END IF
676  END IF
677  IF( colequ .AND. info.EQ.0 ) THEN
678  rcmin = bignum
679  rcmax = zero
680  DO 20 j = 1, n
681  rcmin = min( rcmin, c( j ) )
682  rcmax = max( rcmax, c( j ) )
683  20 CONTINUE
684  IF( rcmin.LE.zero ) THEN
685  info = -14
686  ELSE IF( n.GT.0 ) THEN
687  colcnd = max( rcmin, smlnum ) / min( rcmax, bignum )
688  ELSE
689  colcnd = one
690  END IF
691  END IF
692  IF( info.EQ.0 ) THEN
693  IF( ldb.LT.max( 1, n ) ) THEN
694  info = -15
695  ELSE IF( ldx.LT.max( 1, n ) ) THEN
696  info = -16
697  END IF
698  END IF
699  END IF
700 *
701  IF( info.NE.0 ) THEN
702  CALL xerbla( 'ZGBSVXX', -info )
703  RETURN
704  END IF
705 *
706  IF( equil ) THEN
707 *
708 * Compute row and column scalings to equilibrate the matrix A.
709 *
710  CALL zgbequb( n, n, kl, ku, ab, ldab, r, c, rowcnd, colcnd,
711  \$ amax, infequ )
712  IF( infequ.EQ.0 ) THEN
713 *
714 * Equilibrate the matrix.
715 *
716  CALL zlaqgb( n, n, kl, ku, ab, ldab, r, c, rowcnd, colcnd,
717  \$ amax, equed )
718  rowequ = lsame( equed, 'R' ) .OR. lsame( equed, 'B' )
719  colequ = lsame( equed, 'C' ) .OR. lsame( equed, 'B' )
720  END IF
721 *
722 * If the scaling factors are not applied, set them to 1.0.
723 *
724  IF ( .NOT.rowequ ) THEN
725  DO j = 1, n
726  r( j ) = 1.0d+0
727  END DO
728  END IF
729  IF ( .NOT.colequ ) THEN
730  DO j = 1, n
731  c( j ) = 1.0d+0
732  END DO
733  END IF
734  END IF
735 *
736 * Scale the right-hand side.
737 *
738  IF( notran ) THEN
739  IF( rowequ ) CALL zlascl2( n, nrhs, r, b, ldb )
740  ELSE
741  IF( colequ ) CALL zlascl2( n, nrhs, c, b, ldb )
742  END IF
743 *
744  IF( nofact .OR. equil ) THEN
745 *
746 * Compute the LU factorization of A.
747 *
748  DO 40, j = 1, n
749  DO 30, i = kl+1, 2*kl+ku+1
750  afb( i, j ) = ab( i-kl, j )
751  30 CONTINUE
752  40 CONTINUE
753  CALL zgbtrf( n, n, kl, ku, afb, ldafb, ipiv, info )
754 *
755 * Return if INFO is non-zero.
756 *
757  IF( info.GT.0 ) THEN
758 *
759 * Pivot in column INFO is exactly 0
760 * Compute the reciprocal pivot growth factor of the
761 * leading rank-deficient INFO columns of A.
762 *
763  rpvgrw = zla_gbrpvgrw( n, kl, ku, info, ab, ldab, afb,
764  \$ ldafb )
765  RETURN
766  END IF
767  END IF
768 *
769 * Compute the reciprocal pivot growth factor RPVGRW.
770 *
771  rpvgrw = zla_gbrpvgrw( n, kl, ku, n, ab, ldab, afb, ldafb )
772 *
773 * Compute the solution matrix X.
774 *
775  CALL zlacpy( 'Full', n, nrhs, b, ldb, x, ldx )
776  CALL zgbtrs( trans, n, kl, ku, nrhs, afb, ldafb, ipiv, x, ldx,
777  \$ info )
778 *
779 * Use iterative refinement to improve the computed solution and
780 * compute error bounds and backward error estimates for it.
781 *
782  CALL zgbrfsx( trans, equed, n, kl, ku, nrhs, ab, ldab, afb, ldafb,
783  \$ ipiv, r, c, b, ldb, x, ldx, rcond, berr,
784  \$ n_err_bnds, err_bnds_norm, err_bnds_comp, nparams, params,
785  \$ work, rwork, info )
786
787 *
788 * Scale solutions.
789 *
790  IF ( colequ .AND. notran ) THEN
791  CALL zlascl2( n, nrhs, c, x, ldx )
792  ELSE IF ( rowequ .AND. .NOT.notran ) THEN
793  CALL zlascl2( n, nrhs, r, x, ldx )
794  END IF
795 *
796  RETURN
797 *
798 * End of ZGBSVXX
799 *
subroutine zgbrfsx(TRANS, EQUED, N, KL, KU, NRHS, AB, LDAB, AFB, LDAFB, IPIV, R, C, B, LDB, X, LDX, RCOND, BERR, N_ERR_BNDS, ERR_BNDS_NORM, ERR_BNDS_COMP, NPARAMS, PARAMS, WORK, RWORK, INFO)
ZGBRFSX
Definition: zgbrfsx.f:442
subroutine zgbtrf(M, N, KL, KU, AB, LDAB, IPIV, INFO)
ZGBTRF
Definition: zgbtrf.f:146
subroutine zlascl2(M, N, D, X, LDX)
ZLASCL2 performs diagonal scaling on a vector.
Definition: zlascl2.f:93
subroutine zlacpy(UPLO, M, N, A, LDA, B, LDB)
ZLACPY copies all or part of one two-dimensional array to another.
Definition: zlacpy.f:105
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine zgbtrs(TRANS, N, KL, KU, NRHS, AB, LDAB, IPIV, B, LDB, INFO)
ZGBTRS
Definition: zgbtrs.f:140
subroutine zgbequb(M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND, AMAX, INFO)
ZGBEQUB
Definition: zgbequb.f:163
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:65
double precision function zla_gbrpvgrw(N, KL, KU, NCOLS, AB, LDAB, AFB, LDAFB)
ZLA_GBRPVGRW computes the reciprocal pivot growth factor norm(A)/norm(U) for a general banded matrix...
Definition: zla_gbrpvgrw.f:119
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55
subroutine zlaqgb(M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND, AMAX, EQUED)
ZLAQGB scales a general band matrix, using row and column scaling factors computed by sgbequ...
Definition: zlaqgb.f:162

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