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### Purpose

PxTRMR2D copies the indicated (sub)matrix of A to the indicated (sub)matrix of B. A and B can have arbitrary block-cyclic distributions: they can be distributed across different process grids, have different blocking factors, etc.

The (sub)matrix to be copied is assumed to be trapezoidal. So only the upper or the lower part will be copied. The other part is unchanged.

Particular care must be taken when the process grid over which matrix A is distributed (call this context A) is disjoint from the process grid over which matrix B is distributed (call this context B). The general rules for which parameters need to be set are as follows:

- All calling processes must have the correct M and N.
- Processes in context A must correctly define all parameters describing A.
- Processes in context B must correctly define all parameters describing B.
- Processes that are not members of context A must pass DESCA(CTXT_) = -1 and need not set other parameters describing A.
- Processes that are not members of context B must pass DESCB(CTXT_) = -1 and need not set other parameters describing B.