ilaenv()

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

ILAENV

Purpose:

!>
!> ILAENV returns problem-dependent parameters for the local
!> environment.  See ISPEC for a description of the parameters.
!>
!> In this version, the problem-dependent parameters are contained in
!> the integer array IPARMS in the common block CLAENV and the value
!> with index ISPEC is copied to ILAENV.  This version of ILAENV is
!> to be used in conjunction with XLAENV in TESTING and TIMING.
!> 

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 !> = 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. !> = 9: maximum size of the subproblems at the bottom of the !> computation tree in the divide-and-conquer algorithm !> =10: ieee NaN arithmetic can be trusted not to trap !> =11: infinity arithmetic can be trusted not to trap !> !> Other specifications (up to 100) can be added later. !>
[in]	NAME	!> NAME is CHARACTER*(*) !> The name of the calling subroutine. !>
[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. !>

Returns

ILAENV

!>          ILAENV is INTEGER
!>          >= 0: the value of the parameter specified by ISPEC
!>          < 0:  if ILAENV = -k, the k-th argument had an illegal value.
!> 

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 )
!> 

Definition at line 148 of file ilaenv.f.

*
*  -- LAPACK test routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER*( * )    NAME, OPTS
      INTEGER            ISPEC, N1, N2, N3, N4
*     ..
*
*  =====================================================================
*
*     .. Intrinsic Functions ..
      INTRINSIC          int, min, real
*     ..
*     .. External Functions ..
      INTEGER            IEEECK
      EXTERNAL           ieeeck
*     ..
*     .. Arrays in Common ..
      INTEGER            IPARMS( 100 )
*     ..
*     .. Common blocks ..
      COMMON             / claenv / iparms
*     ..
*     .. Save statement ..
      SAVE               / claenv /
*     ..
*     .. Executable Statements ..
*
      IF( ispec.GE.1 .AND. ispec.LE.5 ) THEN
*
*        Return a value from the common block.
*
         IF ( name(2:6).EQ.'GEQR ' ) THEN
            IF (n3.EQ.2) THEN
               ilaenv = iparms( 2 )
            ELSE
               ilaenv = iparms( 1 )
            END IF
         ELSE IF ( name(2:6).EQ.'GELQ ' ) THEN
            IF (n3.EQ.2) THEN
               ilaenv = iparms( 2 )
            ELSE
               ilaenv = iparms( 1 )
            END IF
         ELSE
            ilaenv = iparms( ispec )
         END IF
*
      ELSE IF( ispec.EQ.6 ) THEN
*
*        Compute SVD crossover point.
*
         ilaenv = int( real( min( n1, n2 ) )*1.6e0 )
*
      ELSE IF( ispec.GE.7 .AND. ispec.LE.9 ) THEN
*
*        Return a value from the common block.
*
         ilaenv = iparms( ispec )
*
      ELSE IF( ispec.EQ.10 ) THEN
*
*        IEEE NaN arithmetic can be trusted not to trap
*
C        ILAENV = 0
         ilaenv = 1
         IF( ilaenv.EQ.1 ) THEN
            ilaenv = ieeeck( 1, 0.0, 1.0 )
         END IF
*
      ELSE IF( ispec.EQ.11 ) THEN
*
*        Infinity arithmetic can be trusted not to trap
*
C        ILAENV = 0
         ilaenv = 1
         IF( ilaenv.EQ.1 ) THEN
            ilaenv = ieeeck( 0, 0.0, 1.0 )
         END IF
*
      ELSE
*
*        Invalid value for ISPEC
*
         ilaenv = -1
      END IF
*
      RETURN
*
*     End of ILAENV
*

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