SYNOPSIS

INTEGER FUNCTION

ILAENV( ISPEC, NAME, OPTS, N1, N2, N3, N4 )

    

CHARACTER*( * ) NAME, OPTS

    

INTEGER ISPEC, N1, N2, N3, N4

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.

ARGUMENTS

ISPEC (input) 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 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 IPARMQ for detailed explanation

NAME (input) CHARACTER*(*)

The name of the calling subroutine, in either upper case or lower case.

OPTS (input) 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 (input) INTEGER

N2 (input) INTEGER N3 (input) INTEGER N4 (input) INTEGER Problem dimensions for the subroutine NAME; these may not all be required.

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 )