Developer Reference for Intel® oneAPI Math Kernel Library - C

Developer Reference

Contents

pjlaenv

Called from the ScaLAPACK symmetric and Hermitian tailored eigen-routines to choose problem-dependent parameters for the local environment.

Syntax

MKL_INT pjlaenv
(
const
MKL_INT*
ictxt
,
const
MKL_INT*
ispec
,
const
char*
name
,
const
char*
opts
,
const
MKL_INT*
n1
,
const
MKL_INT*
n2
,
const
MKL_INT*
n3
,
const
MKL_INT*
n4
);
Include Files
  • mkl.h
Description
pjlaenv
 is called from the ScaLAPACK symmetric and Hermitian tailored eigen-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, though not optimal, performance on many of the currently available computers. You are encouraged to modify this subroutine to set the tuning parameters for your particular machine using the option and problem size information in the arguments.
Input Parameters
ispec
(global input) Specifies the parameter to be returned as the value of
pjlaenv
.
= 1: the data layout blocksize;
= 2: the panel blocking factor;
= 3: the algorithmic blocking factor;
= 4: execution path control;
= 5: maximum size for direct call to the LAPACK routine.
name
(global input) The name of the calling subroutine, in either upper case or lower case.
opts
(global input) 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
,
n2
,
n3
, and
n4
(global input) Problem dimensions for the subroutine name; these may not all be required. At present, only
n1
 is used, and it (
n1
) is used only for
'TTRD'
.
Output Parameters
result
(global or local output)
>= 0: the value of the parameter specified by
ispec
.
< 0: if
pjlaenv
 = -
k
, the
k
-th argument had an illegal value. Most parameters set via a call to
pjlaenv
 must be identical on all processors and hence
pjlaenv
 will return the same value to all procesors (i.e. global output). However some, in particular, the panel blocking factor can be different on each processor and hence
pjlaenv
 can return different values on different processors (i.e. local output).
Application Notes
The following conventions have been used when calling
pjlaenv
 from the ScaLAPACK 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
    , and
    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.
    1. The parameter value returned by
      pjlaenv
       is checked for validity in the calling subroutine. For example,
      pjlaenv
       is used to retrieve the optimal blocksize for
      STRTRI
       as follows: 
      NB = pjlaenv( 1, 'STRTRI', UPLO // DIAG, N, -1, -1, -1 );
IF( NB>=1 ) {
   NB = MAX( 1, N );
}
pjlaenv
 is patterned after
ilaenv
 and keeps the same interface in anticipation of future needs, even though
pjlaenv
 is only sparsely used at present in ScaLAPACK. Most ScaLAPACK codes use the input data layout blocking factor as the algorithmic blocking factor - hence there is no need or opportunity to set the algorithmic or data decomposition blocking factor.
pXYYtevx.f
 and
pXYYtgvx.f
 and
pXYYttrd.f
 are the only codes which call
pjlaenv
.
pXYYtevx.f
 and
pXYYtgvx.f
 redistribute the data to the best data layout for each transformation.
pXYYttrd.f
 uses a data layout blocking factor of 1.

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.