Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
blacs_set
Sets values that BLACS use for internal defaults.
Syntax
call blacs_set ( icontxt , what , val )
Input Parameters
icontxt
INTEGER.
For values of what that are tied to a particular context, this parameter is the integer handle indicating the context. Otherwise, ignored.
what
INTEGER.
Indicates what BLACS internal(s) should be set. Present values are:
1 = Set the BLACS message ID range
11 = Number of rings for multiring broadcast topology to use
12 = Number of branches for general tree broadcast topology to use
13 = Number of rings for multiring combine topology to use
14 = Number of branches for general tree combine topology to use
15 = Force topologies to be repeatable or not
16 = Force topologies to be heterogenous coherent or not
val
INTEGER.
Array of dimension (*). Indicates the value(s) the internals should be set to. The specific meanings depend on what values.
Description
This routine sets the BLACS internal defaults depending on what values:
what = 1
Setting the BLACS message ID range.
If you wish to mix the BLACS with other message-passing packages, restrict the BLACS to a certain message ID range not to be used by the non-BLACS routines. The message ID range must be set before the first call to blacs_gridinit (Assigns available processes into BLACS process grid.) or blacs_gridmap (Maps available processes into BLACS process grid.) . Subsequent calls will have no effect. Because the message ID range is not tied to a particular context, the parameter icontxt is ignored, and val is defined as:
VAL (input) array of dimension (2)
VAL(1) : The smallest message ID (also called message type or message tag) the BLACS should use.
VAL(2) : The largest message ID (also called message type or message tag) the BLACS should use.
what = 11
Set number of rings for TOP = 'M' (multiring broadcast).This quantity is tied to a context, so icontxt is used, and val is defined as:
VAL (input) array of dimension (1)
VAL(1) : The number of rings for multiring topology to use.
what = 12
Set number of branches for TOP = 'T' (general tree broadcast). This quantity is tied to a context, so icontxt is used, and val is defined as:
VAL (input) array of dimension (1)
VAL(1) : The number of branches for general tree topology to use.
what = 13
Set number of rings for TOP = 'M' (multiring combine).This quantity is tied to a context, so icontxt is used, and val is defined as:
VAL (input) array of dimension (1)
VAL(1) : The number of rings for multiring topology to use.
what = 14
Set number of branches for TOP = 'T' (general tree gather). This quantity is tied to a context, so icontxt is used, and val is defined as:
VAL (input) array of dimension (1)
VAL(1) : The number of branches for general tree topology to use.
what = 15
Force topologies to be repeatable or not (see Repeatability and Coherence for more information about repeatability).
VAL (input) array of dimension (1)
VAL(1) = 0 (default)
Topologies are not required to be repeatable.
\(VAL(1) \ne 0\)
All used topologies are required to be repeatable, which might degrade performance.
what = 16
Force topologies to be heterogenous coherent or not (see Repeatability and Coherence for more information about coherence).
VAL (input) array of dimension (1)
VAL(1) = 0 (default)
Topologies are not required to be heterogenous coherent.
\(VAL(1) \ne 0\)
All used topologies are required to be heterogenous coherent, which might degrade performance.