processes managed by MPI and BLACS process grid concept

[gocanal]

Hello,
Would appreciate if someone could confirm my assumption - I am using MPI:

Q1.
- the number of processes created by MPI should be at least the same as the number in the BLACS process grid.

For example, if I create a 2x2 process grid using Cblacs_gridinit (), then I should have 4 MPI processes (for example, I should run my program with this command "mpirun -n 4 myprogram).

And Cblacs_pinfo() will return the number of the processes available in the MPI group.

Am I correct?

Q1.
- Cblacs_gridinit should be run only in the 'main' process (for example, MPI rank = 0).

Am I correct?

But I saw some sample applications, Cblacs_gridinit is run in every process. (reference https://andyspiros.wordpress.com/2011/0 ... cs-with-c/)

many thanks
canal

[gocanal]

according to https://wiki.gwdg.de/index.php/ScaLAPACK, the number of processes created in MPI group is what BLACS process grid can use.