Developer Reference

Contents

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
, as discussed in Description below
.
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
or
blacs_gridmap
. 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)
INTEGER
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)
INTEGER
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)
INTEGER
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)
INTEGER
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)
INTEGER
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)
INTEGER
array of dimension (1)
VAL(1) = 0
(default)
Topologies are not required to be repeatable.
VAL(1)
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)
INTEGER
array of dimension (1)
VAL(1) = 0
(default)
Topologies are not required to be heterogenous coherent.
VAL(1)
0
All used topologies are required to be heterogenous coherent, which might degrade performance.

Product and Performance Information

1

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