ilaenv.f(3)

NAME
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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