NAME

       ilaenv2stage - ilaenv2stage: tuning parameters for 2-stage eig

SYNOPSIS

   Functions
       integer function ilaenv2stage (ispec, name, opts, n1, n2, n3, n4)
           ILAENV2STAGE

Detailed Description

Function Documentation

   integer function ilaenv2stage (integer ispec, character*( * ) name, character*( * ) opts, integer n1, integer
       n2, integer n3, integer n4)
       ILAENV2STAGE

       Purpose:

            ILAENV2STAGE is called from the LAPACK routines to choose problem-dependent
            parameters for the local environment.  See ISPEC for a description of
            the parameters.
            It sets problem and machine dependent parameters useful for *_2STAGE and
            related subroutines.

            ILAENV2STAGE returns an INTEGER
            if ILAENV2STAGE >= 0: ILAENV2STAGE returns the value of the parameter
                                  specified by ISPEC
            if ILAENV2STAGE < 0:  if ILAENV2STAGE = -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 for the 2-stage solvers. 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
                     ILAENV2STAGE.
                     = 1: the optimal blocksize nb for the reduction to BAND

                     = 2: the optimal blocksize ib for the eigenvectors
                          singular vectors update routine

                     = 3: The length of the array that store the Housholder
                          representation for the second stage
                          Band to Tridiagonal or Bidiagonal

                     = 4: The workspace needed for the routine in input.

                     = 5: For future release.

           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.

           Nick R. Papior

       Further Details:

             The following conventions have been used when calling ILAENV2STAGE
            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 ILAENV2STAGE is checked for validity in
                 the calling subroutine.

Author

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Version 3.12.0                              Sun Jul 20 2025 01:40:05                             ilaenv2stage(3)