ilaenv()

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

ILAENV

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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

[in]	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 !>
[in]	NAME	!> NAME is CHARACTER*(*) !> The name of the calling subroutine, in either upper case or !> lower case. !>
[in]	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'. !>
[in]	N1	!> N1 is INTEGER !>
[in]	N2	!> N2 is INTEGER !>
[in]	N3	!> N3 is INTEGER !>
[in]	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 )
!>