Removed call to set that is used in DomainDecomposition.

[gtribello]

This addresses issues #1025 @GiovanniBussi

Description

This commit removes the call to set that is discussed in issue #1025. I don't see that this making a noticeable difference to performance when compared with master but I am possibly not running on the correct setup.

Target release

I would like my code to appear in release 2.10

Type of contribution

• [x ] changes to code or doc authored by PLUMED developers, or additions of code in the core or within the default modules
• [ ] changes to a module not authored by you
• [ ] new module contribution or edit of a module authored by you

Copyright

• [x ] I agree to transfer the copyright of the code I have written to the PLUMED developers or to the author of the code I am modifying.

• [ ] the module I added or modified contains a COPYRIGHT file with the correct license information. Code should be released under an open source license. I also used the command cd src && ./header.sh mymodulename in order to make sure the headers of the module are correct.

Tests

• [ ] I added a new regtest or modified an existing regtest to validate my changes.
• [ x] I verified that all regtests are passed successfully on GitHub Actions.

[carlocamilloni]

@gtribello @gbussi on my big system (where I use 4 mpi) this is actually slower than master this: PLUMED: 3 Waiting for data 2001 1.161034 master: PLUMED: 3 Waiting for data 2001 0.713679

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (9faf503) 84.11% compared to head (f7be61b) 84.11%.

:exclamation: Current head f7be61b differs from pull request most recent head 5424858. Consider uploading reports for the commit 5424858 to get more accurate results

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1026 +/- ## ========================================== - Coverage 84.11% 84.11% -0.01% ========================================== Files 614 614 Lines 56664 56663 -1 ========================================== - Hits 47664 47663 -1 Misses 9000 9000 ```

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[GiovanniBussi]

@carlocamilloni I think it's impossible. Are you sure you are comparing the right versions?

I mean: this change alone basically replaces a function call which does something + sets an element in an array with an explicit instruction that directly sets that element. Am I right @gtribello ?

[gtribello]

I agree @GiovanniBussi. The fact that it is slower is very strange.

[carlocamilloni]

yes you are right, with mpi in comparison to openMP (that is how I usually ran this test) the variability is much larger on the 2,000 steps that i use for this test. In this respect the branch does not make any significant difference