ilaenv(3P) Sun Performance Library ilaenv(3P)NAMEilaenv - The name of the calling subroutine, in either upper case or
lower case.
SYNOPSIS
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);
PURPOSEilaenv 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 param‐
eters 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.
ARGUMENTS
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 crossover 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
dimension 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 bidiago‐
nal form, if max(m,n)/min(m,n) exceeds this value, a QR fac‐
torization 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, concatenated
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 subroutine
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.
FURTHER DETAILS
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 dimensions 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 )
6 Mar 2009 ilaenv(3P)
