NAME

NAME

The name of the calling subroutine, in either upper case or lower case. =head1 SYNOPSIS

  INTEGER FUNCTION ILAENV( ISPEC, NAME, OPTS, N1, N2, N3, N4)
  CHARACTER * 1 NAME(*), OPTS(*)
  INTEGER ISPEC, N1, N2, N3, N4

  INTEGER*8 FUNCTION ILAENV_64( ISPEC, NAME, OPTS, N1, N2, N3, N4)
  CHARACTER * 1 NAME(*), OPTS(*)
  INTEGER*8 ISPEC, N1, N2, N3, N4

F95 INTERFACE

  INTEGER FUNCTION ILAENV( ISPEC, NAME, OPTS, N1, N2, N3, N4)
  CHARACTER(LEN=1), DIMENSION(:) :: NAME, OPTS
  INTEGER :: ISPEC, N1, N2, N3, N4

  INTEGER(8) FUNCTION ILAENV_64( ISPEC, NAME, OPTS, N1, N2, N3, N4)
  CHARACTER(LEN=1), DIMENSION(:) :: NAME, 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);

PURPOSE

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.

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 bidiagonal form, if max(m,n)/min(m,n) exceeds this value, a QR factorization 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 )