10.2 Communication Class

The Communication Class is used to wrap the communication calls to other packages from the CÆSAR Code Package. It also contains serial versions of the routines so that CÆSAR may be run without any external packages on a serial platform.

Communication public procedures:

	Fundamental procedures
	Initialize		Initializes communication.
	Finalize		Finalizes communication.
	Valid_State		Returns false iff the communication is in an invalid state.
	Operations
	Abort		Stops execution on all processors.
	Assemble		Takes a variable that is distributed across all the processors and pulls it together (assembles it) on the IO PE. This is the opposite of the Distribute procedure.
	Broadcast		Sets a variable on all the processors to a value on the IO PE.
	Distribute		Takes a variable on the IO PE and divides it up (distributes it) among all the processors. This is the opposite of the Assemble procedure.
	Gather		Transforms one distributed variable into another distributed variable, according to an indirection index. No collisions are possible, since this call is effectively pulling values out of a distributed variable, and there is a different location for each pulled value. This is the opposite of the Scatter procedure.
	Global Reductions		Global operations that require communication with all the processors, such as SUM, ALL, etc.
	Output		Outputs information about the communication set-up.
	Output_Test		Outputs the result of a test.
	Parallel_Write		Outputs data that is distributed across the processors.
	Scatter_OP		Transforms one distributed variable into another distributed variable, according to an indirection index. Collisions are possible, since this call is effectively putting values into a distributed variable, and more than one value can go into the same location. Therefore, a combination operator, OP, must be specified. Allowed values for OP are: AND, MAX, MIN, OR, or SUM. This is the opposite of the Gather procedure.

Communication public defined types:

Communication_type

The Communication Class variable type.

Communication public variables:

	delta_PE_IO_PE		Kronecker delta (PE, IO_PE).
	IO_PE		The PE number which is allowed to do I/O.
	NPEs		Total number of PEs (1 for serial runs).
	Parallel		True for parallel runs, false for serial runs.
	Parallel_Library		The name of the parallel communication library.
	Serial		True for serial runs, false for parallel runs.
	Scope		Global scope for PGSLib - not really utilized yet.
	this_is_IO_PE		True on any PE which is allowed to perform I/O operations.
	this_is_not_IO_PE		True on any PE which is not allowed to perform I/O operations.
	this_PE		The PE number for this processor (in the range ).

The Communication Class code listing contains additional documentation. The Communication Class also contains a Unit Test Program.