ILAENV (3lapack)

i called from the LAPACK routines to choose problem-dependent parameters for the local environment

SYNOPSIS

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

      CHARACTER*(  * ) NAME, OPTS

      INTEGER      ISPEC, N1, N2, N3, 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) 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 = 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.

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

  OPTS    (input) 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      (input) INTEGER
          N2      (input) INTEGER N3      (input) INTEGER N4      (input)
          INTEGER 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.

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 )