Parallel MODFLOW

Fix common issues when running iMODFLOW & iMOD-WQ codes with MPI.

SMPD errors

Especially if you're running on Windows, you might get (rather cryptic) errors in the vein off:

Unable to start the local smpd manager

Error while connecting to host, No connection could be made because the
target machine actively refused it.

A possible cause is that the path to the smpd.exe, which is a parallel process manager, isn't the right one for the MPI version you're using. The MODFLOW models are generally running with a version of MPICHI2 (https://www.mpich.org/). It's not uncommon, however, to have multiple implementations of MPI installed.

To check, run:

where smpd

Which e.g. returns:

C:\Program Files (x86)\Common Files\Intel\Shared Libraries\redist\ia32_win\mpirt\smpd.exe c:\Program
Files\MPICH2\bin\smpd.exe

Here, there's two versions installed: the Intel version, and the MPICH2 version. In this case, the Intel version is on top, and which generally be called first. Then, when trying to run the model, it's expecting the MPICH2 version instead, and it won't run.

To address this, you can run:

c:\Program Files\MPICH2\bin\smpd.exe -install

This should promote it to the top of the list when you run where again.

Or, just remove it from your PATH if possible. Now, if you run mpiexec.exe, it'll use the right version of smpd.exe.