psb_sum — Global sum

call psb_sum(ctxt, dat [, root, mode, request])

This subroutine implements a sum reduction operation based on the underlying communication library.

Type:: Synchronous.
On Entry
ctxt: the communication context identifying the virtual parallel machine.
Scope: global.
Type: required.
Intent: in.
Specified as: an integer variable.
dat: The local contribution to the global sum.
Scope: global.
Type: required.
Intent: inout.
Specified as: an integer, real or complex variable, which may be a scalar, or a rank 1 or 2 array. Type, kind, rank and size must agree on all processes.
root: Process to hold the final sum, or -1 to make it available on all processes.
Scope: global.
Type: optional.
Intent: in.
Specified as: an integer value -1 <= root <= np - 1, default -1.
mode: Whether the call is started in non-blocking mode and completed later, or is executed synchronously.
Scope: global.
Type: optional.
Intent: in.
Specified as: an integer, with the value determined by the bitwise OR of psb_collective_start_, psb_collective_end_. Default: both fields are selected (i.e. require synchronous completion).
request: A request variable to check for operation completion.
Scope: local.
Type: optional.
Intent: inout.
If mode does not specify synchronous completion, then this variable must be present.

On Return
dat: On destination process(es), the result of the sum operation.
Scope: global.
Type: required.
Intent: inout.
Specified as: an integer, real or complex variable, which may be a scalar, or a rank 1 or 2 array.
Type, kind, rank and size must agree on all processes.
request: A request variable to check for operation completion.
Scope: local.
Type: optional.
Intent: inout.
If mode does not specify synchronous completion, then this variable must be present.

Notes

The dat argument is both input and output, and its value may be changed even on processes different from the final result destination.
The dat argument may also be a long integer scalar.