pdgemr2d: copy between grids

Hello,

I'd like to accomplish the following on a cluster-computer with nproc processors:

1. define two blacs grids, the first of the form p x q = nprocs, the second of the form 1 x 1, which is also just the root process

2. use pdgemr2d to copy a distributed matrix from the first grid to the second

I am already stuck at point 1.

So here are my questions:

a)  Do I have to initialize two MPI communicators and define the blacs contexts in these? 

b) If not, how do I create two separate blacs contexts?

Thanks a lot in advance!

Chris