Fixed code that verifies lshape while using is_split

[Mystic-Slice]

Description

The reuse of gshape array as the receiving buffer made the code a bit too difficult to understand. So, created a new array neighbour_shape to hold, well...., the neighbour's shape.

The use of MPI.SUM, to find if any process has encountered a mismatch in local shapes with its neighbour, leads to errors because of integer limitations. When two or more processes find a mismatch, the huge negative values are added together and I guess because of integer overflow, they disappear into the unknown and finally, we are left with a positive value. So, it does not create any errors when it should. This can be easily solved by using MPI.MIN instead.

One more thing that I don't understand is, why gshape[i] is allowed to be one less than lshape[i] in line 405. I know there must be a reason for it. I just don't understand why.

Code snippet:

import heat as ht
import torch

rank = ht.communication.MPI_WORLD.rank
dim = rank+1

larray = [[0]*dim]*dim
print("Rank", rank, larray)

d = ht.array(larray, is_split=0)

# literally any operation that involves communication 
# between processes will crash
# like this simple print statement
print(d)

Due Diligence

• [ ] All split configurations tested
• [ ] Multiple dtypes tested in relevant functions
• [ ] Documentation updated (if needed)
• [ ] Updated changelog.md under the title "Pending Additions"

Does this change modify the behaviour of other functions? If so, which?

no

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Legend

[Mystic-Slice]

Changes moved to a different branch. Refer https://github.com/helmholtz-analytics/heat/pull/1034