# blacs_get

Gets values that BLACS use for internal defaults.

## Syntax

call blacs_get( icontxt, what, val )

## Input Parameters

icontxt | INTEGER. On 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 returned in val. 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 is icontxt what = 11 : Number of rings multiring topology is presently using what = 12 : Number of branches general tree topology is presently using.

## 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 for `TOP = 'M'` (multiring broadcast)

- The number of branches for `TOP = 'T'` (general tree broadcast/general tree gather).

## See Also

BLACS Routines Usage Example
Parent topic: Initialization Routines