Contents
ilaenv - The name of the calling subroutine, in either upper
case or lower case.
INTEGER FUNCTION ILAENV(ISPEC, NAME, OPTS, N1, N2, N3, N4)
CHARACTER * 6 NAME CHARACTER * 4 OPTS
INTEGER ISPEC, N1, N2, N3, N4
INTEGER*8 FUNCTION ILAENV_64(ISPEC, NAME, OPTS, N1, N2, N3, N4)
CHARACTER * 6 NAME CHARACTER * 4 OPTS
INTEGER*8 ISPEC, N1, N2, N3, N4
F95 INTERFACE
INTEGER FUNCTION ILAENV(ISPEC, NAME, OPTS, N1, N2, N3, N4)
CHARACTER(LEN=6) :: NAME CHARACTER(LEN=4) :: OPTS
INTEGER :: ISPEC, N1, N2, N3, N4
INTEGER(8) FUNCTION ILAENV_64(ISPEC, NAME, OPTS, N1, N2, N3, N4)
CHARACTER(LEN=6) :: NAME CHARACTER(LEN=4) :: OPTS
INTEGER(8) :: ISPEC, N1, N2, N3, N4
C INTERFACE
#include <sunperf.h>
int ilaenv(int ispec, char *name, char *opts, int n1, int
n2, int n3, int n4);
long ilaenv_64(long ispec, char *name, char *opts, long n1,
long n2, long n3, long n4);
ilaenv is called from the LAPACK routines to choose
problem-dependent parameters for the local environment. See
ISPEC for a description of the parameters.
This version provides a set of parameters which should give
good, but not optimal, performance on many of the currently
available computers. Users are encouraged to modify this
subroutine to set the tuning parameters for their particular
machine using the option and problem size information in the
arguments.
This routine will not function correctly if it is converted
to all lower case. Converting it to all upper case is
allowed.
ISPEC (input)
Specifies the parameter to be returned as the
value of ILAENV. = 1: the optimal blocksize; if
this value is 1, an unblocked algorithm will give
the best performance. = 2: the minimum block size
for which the block routine should be used; if the
usable block size is less than this value, an
unblocked routine should be used. = 3: the cross-
over point (in a block routine, for N less than
this value, an unblocked routine should be used) =
4: the number of shifts, used in the nonsymmetric
eigenvalue routines = 5: the minimum column dimen-
sion for blocking to be used; rectangular blocks
must have dimension at least k by m, where k is
given by ILAENV(2,...) and m by ILAENV(5,...) =
6: the crossover point for the SVD (when reducing
an m by n matrix to bidiagonal form, if
max(m,n)/min(m,n) exceeds this value, a QR factor-
ization is used first to reduce the matrix to a
triangular form.) = 7: the number of processors
= 8: the crossover point for the multishift QR and
QZ methods for nonsymmetric eigenvalue problems.
= 9: maximum size of the subproblems at the bottom
of the computation tree in the divide-and-conquer
algorithm (used by xGELSD and xGESDD) =10: ieee
NaN arithmetic can be trusted not to trap
=11: infinity arithmetic can be trusted not to
trap
NAME (input)
The name of the calling subroutine, in either
upper case or lower case.
OPTS (input)
The character options to the subroutine NAME, con-
catenated into a single character string. For
example, UPLO = 'U', TRANS = 'T', and DIAG = 'N'
for a triangular routine would be specified as
OPTS = 'UTN'.
N1 (input)
INTEGER
N2 (input)
INTEGER
N3 (input)
INTEGER
N4 (input)
INTEGER
N1, N2, N3, N4 are problem dimensions for the sub-
routine NAME; these may not all be required.
>= 0: the value of the parameter specified by
ISPEC
< 0: if ILAENV = -k, the k-th argument had an
illegal value.
< 0: if ILAENV = -k, the k-th argument had an
illegal value.
The following conventions have been used when calling ILAENV
from the LAPACK routines:
1) OPTS is a concatenation of all of the character options
to
subroutine NAME, in the same order that they appear in
the
argument list for NAME, even if they are not used in
determining
the value of the parameter specified by ISPEC.
2) The problem dimensions N1, N2, N3, N4 are specified in
the order
that they appear in the argument list for NAME. N1 is
used
first, N2 second, and so on, and unused problem dimen-
sions are
passed a value of -1.
3) The parameter value returned by ILAENV is checked for
validity in
the calling subroutine. For example, ILAENV is used to
retrieve
the optimal blocksize for STRTRI as follows:
NB = ILAENV( 1, 'STRTRI', UPLO // DIAG, N, -1, -1, -1 )
IF( NB.LE.1 ) NB = MAX( 1, N )