ESMF_ILAENV Function

function ESMF_ILAENV(ISPEC, NAME, OPTS, N1, N2, N3, N4)

\brief \b ESMF_ILAENV \htmlonly Download ESMF_ILAENV + dependencies [TGZ] [ZIP] [TXT] \endhtmlonly \par Purpose:

\verbatim

ESMF_ILAENV is called from the LAPACK routines to choose problem-dependent parameters for the local environment. See ISPEC for a description of the parameters.

ESMF_ILAENV returns an INTEGER if ESMF_ILAENV >= 0: ESMF_ILAENV returns the value of the parameter specified by ISPEC if ESMF_ILAENV < 0: if ESMF_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. \endverbatim \param[in] ISPEC \verbatim ISPEC is INTEGER Specifies the parameter to be returned as the value of ESMF_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 ESMF_ILAENV(2,…) and m by ESMF_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 NaN arithmetic can be trusted not to trap =11: infinity arithmetic can be trusted not to trap 12 <= ISPEC <= 16: xHSEQR or one of its subroutines, see ESMF_IPARMQ for detailed explanation \endverbatim

\param[in] NAME \verbatim NAME is CHARACTER() The name of the calling subroutine, in either upper case or lower case. \endverbatim

\param[in] OPTS \verbatim 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’. \endverbatim

\param[in] N1 \verbatim N1 is INTEGER \endverbatim

\param[in] N2 \verbatim N2 is INTEGER \endverbatim

\param[in] N3 \verbatim N3 is INTEGER \endverbatim

\param[in] N4 \verbatim N4 is INTEGER Problem dimensions for the subroutine NAME; these may not all be required. \endverbatim \author Univ. of Tennessee \author Univ. of California Berkeley \author Univ. of Colorado Denver \author NAG Ltd. \date November 2011 \ingroup auxOTHERauxiliary \par Further Details:

\verbatim

The following conventions have been used when calling ESMF_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 ESMF_ILAENV is checked for validity in the calling subroutine. For example, ESMF_ILAENV is used to retrieve the optimal blocksize for STRTRI as follows:

 NB = ESMF_ILAENV( 1, 'STRTRI', UPLO
 IF( NB.LE.1 ) NB = MAX( 1, N )

\endverbatim

Arguments

Return Value integer