ilaenv(3)                  Library Functions Manual                  ilaenv(3)

NAME
       ilaenv - ilaenv: tuning parameters

SYNOPSIS
   Functions
       integer function ilaenv (ispec, name, opts, n1, n2, n3, n4)
           ILAENV

Detailed Description
Function Documentation
   integer function ilaenv (integer ispec, character*( * ) name, character*( *
       ) opts, integer n1, integer n2, integer n3, integer n4)
       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 infinity and NaN arithmetic can be trusted not to trap
           !>          =11: infinity arithmetic can be trusted not to trap
           !>          12 <= ISPEC <= 17:
           !>               xHSEQR or related 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.

       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 161 of file ilaenv.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

LAPACK                          Version 3.12.0                       ilaenv(3)