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  if ILAENV2STAGE < 0:  if ILAENV2STAGE = -k, the k-th argument had an 


 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.

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.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Nick R. Papior

July 2017

  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.