Failed expression ranksAtInterface ! = 0

I do fluid-fluid coupling calculations. Initialization can be passed when both fluid solvers are parallel, but one with parallel and the other without parallel cannot be initialized

Failed expression: ranksAtInterface ! = 0

What’s happening?
Thank you

Welcome @lixiaole2017!

This is definitely not a user-friendly error message and we should improve it. But in order to do this, we need to be able to reproduce the problem.

Could you please give more details? Which solvers are you using? Which preCICE version? Any other details about the case you are running?

@lixiaole2017 did you manage to solve this? In a newer preCICE version (v2.1 or later), this should be much better.

This is actually an assertion deep in the partitioning package.
As @Makis said, this should be an error with a user-friendly message.

What this means is that when running in parallel, there is no overlap between the meshes of both solvers.

If it still fails running both solvers in on a single core each, then this is a strong indicator that the meshes are not describing the same geometry. The error message will be different in that case
Otherwise, it could also be that the interface meshes are super coarse, which could lead to problems.