I think the behaviour of parameters['allow_extrapolation']=True maybe requires a revision. My opinion is that it should allow only extrapolation out of a global mesh not outside a partition.
Current behaviour reflects practical point of view - when process does not know some value it extrapolates. But from mathematical point of view it should be guaranteed that user's program behaves consistently if run by 1 or more processes (at least in the case of a single-instruction code like in the bug description). Also like Mikael noted it computes rubbish when extrapolating between partitions.
I think the behaviour of parameters[ 'allow_ extrapolation' ]=True maybe requires a revision. My opinion is that it should allow only extrapolation out of a global mesh not outside a partition.
Current behaviour reflects practical point of view - when process does not know some value it extrapolates. But from mathematical point of view it should be guaranteed that user's program behaves consistently if run by 1 or more processes (at least in the case of a single-instruction code like in the bug description). Also like Mikael noted it computes rubbish when extrapolating between partitions.
Jan