# ilaenv.f - Man Page

TESTING/LIN/ilaenv.f

## Synopsis

### Functions/Subroutines

integer function **ilaenv** (ispec, name, opts, n1, n2, n3, n4)**ILAENV**

integer function **ilaenv2stage** (ispec, name, opts, n1, n2, n3, n4)

## Function/Subroutine Documentation

### integer function ilaenv (integer ispec, character*( * ) name, character*( * ) opts, integer n1, integer n2, integer n3, integer n4)

**ILAENV**

**Purpose:**

ILAENV returns problem-dependent parameters for the local environment. See ISPEC for a description of the parameters. In this version, the problem-dependent parameters are contained in the integer array IPARMS in the common block CLAENV and the value with index ISPEC is copied to ILAENV. This version of ILAENV is to be used in conjunction with XLAENV in TESTING and TIMING.

**Parameters***ISPEC*ISPEC is 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 = 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 subproblems at the bottom of the computation tree in the divide-and-conquer algorithm =10: ieee NaN arithmetic can be trusted not to trap =11: infinity arithmetic can be trusted not to trap Other specifications (up to 100) can be added later.

*NAME*NAME is CHARACTER*(*) The name of the calling subroutine.

*OPTS*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'.

*N1*N1 is INTEGER

*N2*N2 is INTEGER

*N3*N3 is INTEGER

*N4*N4 is INTEGER Problem dimensions for the subroutine NAME; these may not all be required.

**Returns**ILAENV

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

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**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 )

Definition at line **148** of file **ilaenv.f**.

### integer function ilaenv2stage (integer ispec, character*( * ) name, character*( * ) opts, integer n1, integer n2, integer n3, integer n4)

Definition at line **244** of file **ilaenv.f**.

## Author

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## Info

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK