ilaenv (l)  Linux Man Pages
ilaenv: is called from the LAPACK routines to choose problemdependent parameters for the local environment
NAME
ILAENV  is called from the LAPACK routines to choose problemdependent parameters for the local environmentSYNOPSIS
 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 problemdependent 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 kth 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 divideandconquer 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 = aqUaq, TRANS = aqTaq, and DIAG = aqNaq for a triangular routine would be specified as OPTS = aqUTNaq.
 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
2) The problem dimensions N1, N2, N3, N4 are specified in the order
3) The parameter value returned by ILAENV is checked for validity in