I am relatively new to MPI (with C), and am having some trouble using MPI_Bcast to send an int to all processes.
In my code, I decide which rank is root within a for loop, where different processes are responsible for different element of the loop. Then, I want to Bcast a result from root to all processes, except all non-root processes do not know who to expect the bcast from, so do not receive it.
The code block looks something like this:
for (iX=start; iX<end; iX++) //start and end are the starting row and ending row for each processes, defined earlier for (int iY=1; iY<nn; iY++) // do some calculations if (some condition) int bcastroot = rank; // initialized above int X = 111; // initialized above else //do other calculations end end MPI_Bcast(&X, 1, MPI_INT, bcastroot, comm); // remainder of code and MPI_FINALIZE When I execute this code, whatever the bcastroot default (value for all non-root processes) competes with root, so X is not broadcast correctly. I do not know the value of X nor can I predict the root beforehand, so I cannot define it in advance.
I have tried initializing bcastroot = -1, then setting it for rank, but this does not work. Is there a way I can Bcast this value without setting root for all processes?
Thanks, JonZor
