# 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

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