ILAENV(l)								 )								 ILAENV(l)

NAME

       ILAENV - i called from the LAPACK routines to choose problem-dependent parameters for the local environment

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.

       This version provides a set of parameters which should give good, but not optimal, performance on many of the currently	available  comput-
       ers.  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  algo-
	       rithm  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 sub-
	       problems at the bottom of the computation tree in the divide-and-conquer algorithm (used by xGELSD and xGESDD) =10: ieee NaN arith-
	       metic can be trusted not to trap
	       =11: infinity arithmetic can be trusted not to trap

       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.

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

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 )

LAPACK version 3.0						   15 June 2000 							 ILAENV(l)