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RedHat 9 (Linux i386) - man page for ilaenv (redhat section l)

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, perfor-
       mance 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  perfor-
	       mance.  = 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  non-
	       symmetric 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 ei-
	       genvalue problems.  = 9: maximum size of the subproblems at the bottom of the com-
	       putation 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

       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)


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