Code overlaps in computing gradients of objective functions removed.

[evgueni-ovtchinnikov]

Changes in this pull request

Got rid of code overlaps in computing gradients of objective functions.

Testing performed

Related issues

fixes #1252

Checklist before requesting a review

• I have performed a self-review of my code
• I have added docstrings/doxygen in line with the guidance in the developer guide
• I have implemented unit tests that cover any new or modified functionality
• The code builds and runs on my machine
• CHANGES.md has been updated with any functionality change

Contribution Notes

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• The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in SIRF (the Work) under the terms and conditions of the Apache-2.0 License.

[KrisThielemans]

some small comments for shorter (and therefore clearer) code). Otherwise, I just suggest addiing some comments on the diff between cSTIR_objectiveFunctionGradient and cSTIR_computeObjectiveFunctionGradient (not obvious from the name!)

[KrisThielemans]

add a doxygen string please.

By the way, does SIRF not use the same convention as STIR, where the output arg gd is placed first?

[evgueni-ovtchinnikov]

doxygen: done

STIR convention: no, SIRF does not use it