psb_init -- Initializes PSBLAS parallel environment

call psb_init(icontxt, np, basectxt, ids)

This subroutine initializes the PSBLAS parallel environment, defining a virtual parallel machine.

Type:

Synchronous.

On Entry

np

Number of processes in the PSBLAS virtual parallel machine.
Scope: global.
Type: optional.
Intent: in.
Specified as: an integer value. Default: use all available processes.

basectxt

the initial communication context. The new context will be defined from the processes participating in the initial one.
Scope: global.
Type: optional.
Intent: in.
Specified as: an integer value. Default: use MPI_COMM_WORLD.

ids

Identities of the processes to use for the new context; the argument is ignored when np is not specified. This allows the processes in the new environment to be in an order different from the original one.
Scope: global.
Type: optional.
Intent: in.
Specified as: an integer array. Default: use the indices $(0\dots np-1)$.

On Return

icontxt

the communication context identifying the virtual parallel machine. Note that this is always a duplicate of basectxt, so that library communications are completely separated from other communication operations.
Scope: global.
Type: required.
Intent: out.
Specified as: an integer variable.

Notes

1. A call to this routine must precede any other PSBLAS call.
2. It is an error to specify a value for $np$ greater than the number of processes available in the underlying base parallel environment.