blacs_get
blacs_get
Gets values that BLACS use for internal defaults.
Syntax
call blacs_get
(
icontxt
,
what
,
val
)
Input Parameters
- icontxt
- INTEGER. On values ofwhatthat 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 returned inval. Present options are:
- what= 0 : Handle indicating default system context.
- what= 1 : The BLACS message ID range.
- what= 2 : The BLACS debug level the library was compiled with.
- what= 10 : Handle indicating the system context used to define the BLACS context whose handle isicontxt.
- what= 11 : Number of rings multiring broadcast topology is presently using.
- what= 12 : Number of branches general tree broadcast topology is presently using.
- what= 13 : Number of rings multiring combine topology is presently using.
- what= 14 : Number of branches general tree combine topology is presently using.
- what= 15 : Whether topologies are forced to be repeatable or not. A non-zero return value indicates that topologies are being forced to be repeatable. See Repeatability and Coherence for more information about repeatability.
- what= 16 : Whether topologies are forced to be heterogenous coherent or not. A non-zero return value indicates that topologies are being forced to be heterogenous coherent. See Repeatability and Coherence for more information about coherence.
Output Parameters
- val
- INTEGER. The value of the BLACS internal.
Description
This routine gets the values that the BLACS are using for internal defaults. Some values are tied to a BLACS context, and some are more general. The most common use is in retrieving a default system context for input into
blacs_gridinit
or blacs_gridmap
. Some systems, such as MPI*, supply their own version of context. For those users who mix system code with BLACS code, a BLACS context should be formed in reference to a system context. Thus, the grid creation routines take a system context as input. If you wish to have strictly portable code, you may use
blacs_get
to retrieve a default system context that will include all available processes. This value is not tied to a BLACS context, so the parameter icontxt
is unused.blacs_get
returns information on three quantities that are tied to an individual BLACS context, which is passed in as icontxt
. The information that may be retrieved is: - The handle of the system context upon which this BLACS context was defined
- The number of rings forTOP = 'M'(multiring broadcast/combine)
- The number of branches forTOP = 'T'(general tree broadcast/general tree gather).
- Whether topologies are being forced to be repeatable or heterogenous coherent.