mesh_get_index returns a value of -1 when a particle lies on mesh minimum boundary

[goodman17c]

The mesh_get_index returns a value of -1 when a particle is at the lower boundary of a mesh in any of space or time. This is problematic for having an initial condition or boundary source. Often, the effect is unnoticed as Python will treat the -1 index to reference the last element of the array without error or warning.

A workaround has been to modify the mesh in the input file with some small perturbation.

[ilhamv]

That is true. The current solution is that users need to move the boundary/point source into the domain by manually specifying it in the mcdc.source.