PMD Restrictions

The computational domain must be simply connected.
Along the domain decomposition axis, physical boundary conditions are assumed to be non-periodic.
The current version of PMD stands for 1D Domain decomposition only which means that subdomain interfaces cannot cross.
The interface normal vectors must be parallel to the domain decomposition axis.
It is up to the user to compute the interface first normal derivatives along the domain decomposition axis.
When using direct parallel solvers, which here are based on the ScaLAPACK library, the BLACS process grid must be square. This means that if Np denotes the process grid dimension, then the size of the PMD process group must be equal to Np**2. However this restriction doesn't stand when using parallel iterative solvers as PCG and Bi-CGstab algorithms.
Parallel PCG and Bi-CGstab methods, has an inconvenient property which is the number of iterations to convergence increases as the number of subdomains grows.