If the user doesn't provide a decomposition, or the user starts with more MPI ranks as the decomposition allows, the Micro Manager could try to come up with a "best effort decomposition".
For $r$ ranks:
- use uniform $n^{dims}=r$ if possible
- otherwise $n*m=r, n>m$ split longest axis (based on bounds) by $n$, and second-longest by $m$.
- otherwise split longest axis by $r$
If the user doesn't provide a decomposition, or the user starts with more MPI ranks as the decomposition allows, the Micro Manager could try to come up with a "best effort decomposition".
For$r$ ranks: