ilaenv.f man page

ilaenv.f —

Synopsis

Functions/Subroutines

INTEGER function ilaenv (ISPEC, NAME, OPTS, N1, N2, N3, N4)
ILAENV

Function/Subroutine Documentation

INTEGER function ilaenv (integerISPEC, character*( * )NAME, character*( * )OPTS, integerN1, integerN2, integerN3, integerN4)

ILAENV

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.

ILAENV returns an INTEGER
if ILAENV >= 0: ILAENV returns the value of the parameter specified by ISPEC
if ILAENV < 0:  if ILAENV = -k, the k-th argument had an illegal value.

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.

Parameters:

ISPEC

ISPEC is INTEGER
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 (DEPRECATED)
= 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 method
     for nonsymmetric eigenvalue problems (DEPRECATED)
= 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
12 <= ISPEC <= 16:
     xHSEQR or one of its subroutines,
     see IPARMQ for detailed explanation

NAME

NAME is CHARACTER*(*)
The name of the calling subroutine, in either upper case or
lower case.

OPTS

OPTS is CHARACTER*(*)
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

N1 is INTEGER

N2

N2 is INTEGER

N3

N3 is INTEGER

N4

N4 is INTEGER
Problem dimensions for the subroutine NAME; these may not all
be required.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

November 2011

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 )

Definition at line 163 of file ilaenv.f.

Author

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Referenced By

ilaenv(3) is an alias of ilaenv.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK