zgbsvxx - compute the solution to system of linear equations A * X = B for general band matrices
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) CHARACTER*1 EQUED, FACT, TRANS INTEGER INFO, LDAB, LDAFB, LDB, LDX, N, NRHS, NPARAMS, N_ERR_BNDS DOUBLE PRECISION RCOND, RPVGRW INTEGER IPIV(*) DOUBLE COMPLEX AB(LDAB,*), AFB(LDAFB,*), B(LDB,*), X(LDX,*), WORK(*) DOUBLE PRECISION R(*), C(*), PARAMS(*), BERR(*), ERR_BNDS_NORM(NRHS,*), ERR_BNDS_COMP(NRHS,*), RWORK(*) SUBROUTINE ZGBSVXX_64(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) CHARACTER*1 EQUED, FACT, TRANS INTEGER*8 INFO, LDAB, LDAFB, LDB, LDX, N, NRHS, NPARAMS, N_ERR_BNDS DOUBLE PRECISION RCOND, RPVGRW INTEGER*8 IPIV(*) DOUBLE COMPLEX AB(LDAB,*), AFB(LDAFB,*), B(LDB,*), X(LDX,*), WORK(*) DOUBLE PRECISION R(*), C(*), PARAMS(*), BERR(*), ERR_BNDS_NORM(NRHS,*), ERR_BNDS_COMP(NRHS,*), RWORK(*) F95 INTERFACE SUBROUTINE GBSVXX(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) INTEGER :: N, KL, KU, NRHS, LDAB, LDAFB, LDB, LDX, N_ERR_BNDS, NPARAMS, INFO CHARACTER(LEN=1) :: FACT, TRANS, EQUED INTEGER, DIMENSION(:) :: IPIV REAL(8), DIMENSION(:,:) :: ERR_BNDS_NORM, ERR_BNDS_COMP REAL(8), DIMENSION(:) :: R, C, BERR, PARAMS, RWORK COMPLEX(8), DIMENSION(:,:) :: AB, AFB, B, X COMPLEX(8), DIMENSION(:) :: WORK REAL(8) :: RCOND, RPVGRW SUBROUTINE GBSVXX_64(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) INTEGER(8) :: N, KL, KU, NRHS, LDAB, LDAFB, LDB, LDX, N_ERR_BNDS, NPARAMS, INFO CHARACTER(LEN=1) :: FACT, TRANS, EQUED INTEGER(8), DIMENSION(:) :: IPIV REAL(8), DIMENSION(:,:) :: ERR_BNDS_NORM, ERR_BNDS_COMP REAL(8), DIMENSION(:) :: R, C, BERR, PARAMS, RWORK COMPLEX(8), DIMENSION(:,:) :: AB, AFB, B, X COMPLEX(8), DIMENSION(:) :: WORK REAL(8) :: RCOND, RPVGRW C INTERFACE #include <sunperf.h> void zgbsvxx (char fact, char trans, int n, int kl, int ku, int nrhs, doublecomplex *ab, int ldab, doublecomplex *afb, int ldafb, int *ipiv, char *equed, double *r, double *c, doublecomplex *b, int ldb, doublecomplex *x, int ldx, double *rcond, double *rpvgrw, double *berr, int n_err_bnds, double *err_bnds_norm, double *err_bnds_comp, int nparams, double *params, int *info); void zgbsvxx_64 (char fact, char trans, long n, long kl, long ku, long nrhs, doublecomplex *ab, long ldab, doublecomplex *afb, long ldafb, long *ipiv, char *equed, double *r, double *c, double- complex *b, long ldb, doublecomplex *x, long ldx, double *rcond, double *rpvgrw, double *berr, long n_err_bnds, double *err_bnds_norm, double *err_bnds_comp, long nparams, double *params, long *info);
Oracle Solaris Studio Performance Library zgbsvxx(3P)
NAME
zgbsvxx - compute the solution to system of linear equations A * X = B
for general band matrices
SYNOPSIS
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)
CHARACTER*1 EQUED, FACT, TRANS
INTEGER INFO, LDAB, LDAFB, LDB, LDX, N, NRHS, NPARAMS, N_ERR_BNDS
DOUBLE PRECISION RCOND, RPVGRW
INTEGER IPIV(*)
DOUBLE COMPLEX AB(LDAB,*), AFB(LDAFB,*), B(LDB,*), X(LDX,*), WORK(*)
DOUBLE PRECISION R(*), C(*), PARAMS(*), BERR(*), ERR_BNDS_NORM(NRHS,*),
ERR_BNDS_COMP(NRHS,*), RWORK(*)
SUBROUTINE ZGBSVXX_64(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)
CHARACTER*1 EQUED, FACT, TRANS
INTEGER*8 INFO, LDAB, LDAFB, LDB, LDX, N, NRHS, NPARAMS, N_ERR_BNDS
DOUBLE PRECISION RCOND, RPVGRW
INTEGER*8 IPIV(*)
DOUBLE COMPLEX AB(LDAB,*), AFB(LDAFB,*), B(LDB,*), X(LDX,*), WORK(*)
DOUBLE PRECISION R(*), C(*), PARAMS(*), BERR(*), ERR_BNDS_NORM(NRHS,*),
ERR_BNDS_COMP(NRHS,*), RWORK(*)
F95 INTERFACE
SUBROUTINE GBSVXX(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)
INTEGER :: N, KL, KU, NRHS, LDAB, LDAFB, LDB, LDX, N_ERR_BNDS, NPARAMS,
INFO
CHARACTER(LEN=1) :: FACT, TRANS, EQUED
INTEGER, DIMENSION(:) :: IPIV
REAL(8), DIMENSION(:,:) :: ERR_BNDS_NORM, ERR_BNDS_COMP
REAL(8), DIMENSION(:) :: R, C, BERR, PARAMS, RWORK
COMPLEX(8), DIMENSION(:,:) :: AB, AFB, B, X
COMPLEX(8), DIMENSION(:) :: WORK
REAL(8) :: RCOND, RPVGRW
SUBROUTINE GBSVXX_64(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)
INTEGER(8) :: N, KL, KU, NRHS, LDAB, LDAFB, LDB, LDX, N_ERR_BNDS,
NPARAMS, INFO
CHARACTER(LEN=1) :: FACT, TRANS, EQUED
INTEGER(8), DIMENSION(:) :: IPIV
REAL(8), DIMENSION(:,:) :: ERR_BNDS_NORM, ERR_BNDS_COMP
REAL(8), DIMENSION(:) :: R, C, BERR, PARAMS, RWORK
COMPLEX(8), DIMENSION(:,:) :: AB, AFB, B, X
COMPLEX(8), DIMENSION(:) :: WORK
REAL(8) :: RCOND, RPVGRW
C INTERFACE
#include <sunperf.h>
void zgbsvxx (char fact, char trans, int n, int kl, int ku, int nrhs,
doublecomplex *ab, int ldab, doublecomplex *afb, int ldafb,
int *ipiv, char *equed, double *r, double *c, doublecomplex
*b, int ldb, doublecomplex *x, int ldx, double *rcond, double
*rpvgrw, double *berr, int n_err_bnds, double *err_bnds_norm,
double *err_bnds_comp, int nparams, double *params, int
*info);
void zgbsvxx_64 (char fact, char trans, long n, long kl, long ku, long
nrhs, doublecomplex *ab, long ldab, doublecomplex *afb, long
ldafb, long *ipiv, char *equed, double *r, double *c, double-
complex *b, long ldb, doublecomplex *x, long ldx, double
*rcond, double *rpvgrw, double *berr, long n_err_bnds, double
*err_bnds_norm, double *err_bnds_comp, long nparams, double
*params, long *info);
PURPOSE
zgbsvxx uses the LU factorization to compute the solution to a com-
plex*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.
ARGUMENTS
FACT (input)
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.
TRANS (input)
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)
N (input)
N is INTEGER
The number of linear equations, i.e., the order of the matrix
A. N >= 0.
KL (input)
KL is INTEGER
The number of subdiagonals within the band of A. KL >= 0.
KU (input)
KU is INTEGER
The number of superdiagonals within the band of A. KU >= 0.
NRHS (input)
NRHS is INTEGER
The number of right hand sides, i.e., the number of columns
of the matrices B and X.
NRHS >= 0.
AB (input/output)
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).
LDAB (input)
LDAB is INTEGER
The leading dimension of the array AB.
LDAB >= KL+KU+1.
AFB (input/output)
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 origi-
nal 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).
LDAFB (input)
LDAFB is INTEGER
The leading dimension of the array AFB.
LDAFB >= 2*KL+KU+1.
IPIV (input/output)
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.
EQUED (input/output)
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.
R (input/output)
R is DOUBLE PRECISION array, dimension (N)
The row scale factors for A. If EQUED = 'R' or 'B', A is mul-
tiplied on the left by diag(R); if EQUED = 'N' or 'C', R is
not accessed. R is an input argument if FACT = 'F'; other-
wise, 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.
C (input/output)
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'; other-
wise, 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.
B (input/output)
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 overwrit-
ten by diag(C)*B.
LDB (input)
LDB is INTEGER
The leading dimension of the array B.
LDB >= max(1,N).
X (output)
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 sys-
tem 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'.
LDX (input)
LDX is INTEGER
The leading dimension of the array X.
LDX >= max(1,N).
RCOND (output)
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 sin-
gular to working precision. Note that the error may still be
small even if this number is very small and the matrix
appears ill- conditioned.
RPVGRW (output)
RPVGRW is DOUBLE PRECISION
Reciprocal pivot growth. On exit, this contains the recipro-
cal 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 unre-
liable. If factorization fails with 0<INFO<=N, then this con-
tains the reciprocal pivot growth factor for the leading INFO
columns of A. In DGESVX, this quantity is returned in
WORK(1).
BERR (output)
BERR is DOUBLE PRECISION array, dimension (NRHS)
Componentwise relative backward error. This is the component-
wise 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).
N_ERR_BNDS (input)
N_ERR_BNDS is INTEGER
Number of error bounds to return for each right hand side and
each type (normwise or componentwise). See ERR_BNDS_NORM and
ERR_BNDS_COMP below.
ERR_BNDS_NORM (output)
ERR_BNDS_NORM is DOUBLE PRECISION array, dimension (NRHS,
N_ERR_BNDS)
For each right-hand side, this array contains information
about various error bounds and condition numbers correspond-
ing to the normwise relative error, which is defined as fol-
lows:
Normwise relative error in the ith solution vector:
max_j (abs(XTRUE(j,i) - X(j,i)))
------------------------------
max_j abs(X(j,i))
The array is indexed by the type of error information as
described below. There currently are up to three pieces of
information returned.
The first index in ERR_BNDS_NORM(i,:) corresponds to the ith
right-hand side.
The second index in ERR_BNDS_NORM(:,err) contains the follow-
ing three fields:
err = 1 "Trust/don't trust" boolean. Trust the answer if the
reciprocal condition number is less than the threshold
sqrt(n) * dlamch('Epsilon').
err = 2 "Guaranteed" error bound: The estimated forward
error, almost certainly within a factor of 10 of the true
error so long as the next entry is greater than the threshold
sqrt(n) * dlamch('Epsilon'). This error bound should only be
trusted if the previous boolean is true.
err = 3 Reciprocal condition number: Estimated normwise
reciprocal condition number. Compared with the threshold
sqrt(n) * dlamch('Epsilon') to determine if the error esti-
mate is "guaranteed". These reciprocal condition numbers are
1 / (norm(Z^{-1},inf) * norm(Z,inf)) for some appropriately
scaled matrix Z.
Let Z = S*A, where S scales each row by a power of the radix
so all absolute row sums of Z are approximately 1.
See Lapack Working Note 165 for further details and extra
cautions.
ERR_BNDS_COMP (output)
ERR_BNDS_COMP is DOUBLE PRECISION array, dimension (NRHS,
N_ERR_BNDS)
For each right-hand side, this array contains information
about various error bounds and condition numbers correspond-
ing to the componentwise relative error, which is defined as
follows:
Componentwise relative error in the ith solution vector:
abs(XTRUE(j,i) - X(j,i))
max_j ----------------------
abs(X(j,i))
The array is indexed by the right-hand side i (on which the
componentwise relative error depends), and the type of error
information as described below. There currently are up to
three pieces of information returned for each right-hand
side. If componentwise accuracy is not requested (PARAMS(3) =
0.0), then ERR_BNDS_COMP is not accessed. If N_ERR_BNDS .LT.
3, then at most the first (:,N_ERR_BNDS) entries are
returned.
The first index in ERR_BNDS_COMP(i,:) corresponds to the ith
right-hand side.
The second index in ERR_BNDS_COMP(:,err) contains the follow-
ing three fields:
err = 1 "Trust/don't trust" boolean. Trust the answer if the
reciprocal condition number is less than the threshold
sqrt(n) * dlamch('Epsilon').
err = 2 "Guaranteed" error bound: The estimated forward
error, almost certainly within a factor of 10 of the true
error so long as the next entry is greater than the threshold
sqrt(n) * dlamch('Epsilon'). This error bound should only be
trusted if the previous boolean is true.
err = 3 Reciprocal condition number: Estimated componentwise
reciprocal condition number. Compared with the threshold
sqrt(n) * dlamch('Epsilon') to determine if the error esti-
mate is "guaranteed". These reciprocal condition numbers are
1 / (norm(Z^{-1},inf) * norm(Z,inf)) for some appropriately
scaled matrix Z.
Let Z = S*(A*diag(x)), where x is the solution for the cur-
rent right-hand side and S scales each row of A*diag(x) by a
power of the radix so all absolute row sums of Z are approxi-
mately 1.
See Lapack Working Note 165 for further details and extra
cautions.
NPARAMS (input)
NPARAMS is INTEGER
Specifies the number of parameters set in PARAMS. If .LE. 0,
the PARAMS array is never referenced and default values are
used.
PARAMS (input/output)
PARAMS is DOUBLE PRECISION array, dimension NPARAMS
Specifies algorithm parameters. If an entry is .LT. 0.0, then
that entry will be filled with default value used for that
parameter. Only positions up to NPARAMS are accessed;
defaults are used for higher-numbered parameters.
PARAMS(LA_LINRX_ITREF_I = 1) : Whether to perform iterative
refinement or not.
Default: 1.0D+0
= 0.0 : No refinement is performed, and no error bounds are
computed.
= 1.0 : Use the extra-precise refinement algorithm.
(other values are reserved for future use)
PARAMS(LA_LINRX_ITHRESH_I = 2) : Maximum number of residual
computations allowed for refinement.
Default: 10
Aggressive: Set to 100 to permit convergence using approxi-
mate factorizations or factorizations other than LU. If the
factorization uses a technique other than Gaussian elimina-
tion, the guarantees in err_bnds_norm and err_bnds_comp may
no longer be trustworthy.
PARAMS(LA_LINRX_CWISE_I = 3) : Flag determining if the code
will attempt to find a solution with small componentwise rel-
ative error in the double-precision algorithm. Positive is
true, 0.0 is false.
Default: 1.0 (attempt componentwise convergence)
WORK (output)
WORK is COMPLEX*16 array, dimension (2*N)
RWORK (output)
RWORK is DOUBLE PRECISION array, dimension (2*N)
INFO (output)
INFO is INTEGER
= 0: Successful exit. The solution to every right-hand side
is guaranteed.
< 0: If INFO = -i, the i-th argument had an illegal value
> 0 and <= N: U(INFO,INFO) is exactly zero. The factoriza-
tion has been completed, but the factor U is exactly singu-
lar, 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 small-
est 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.
7 Nov 2015 zgbsvxx(3P)