Feature 2708 mvmode merge flag default

[davidalbo]

Expected Differences

• Do these changes introduce new tools, command line arguments, or configuration file options? [No]
  

• Do these changes modify the structure of existing or add new output data types (e.g. statistic line types or NetCDF variables)? [No]
  

Pull Request Testing

• Describe testing already performed for these changes:
  I did these tests:

1. create a config with a field that does not specify merge_flag/merge_thresh and make sure it defaults to NONE.
2. create a config with a field that has merge_flag but no merge_thresh and observe the error exit.
3. create a config with a field that has merge_thresh but no merge_flag and observe the error exit.

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  Take a previous test case (if still around) and modify the config file in the above 3 ways to see what happens.

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• Do these changes include sufficient testing updates? [Yes ]

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Please complete this pull request review by [October 17 2023].
  

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[hertneky]

@davidalbo Should I be testing this also? If so, where is it installed? Or am I just reviewing the code changes?

[davidalbo]

@hertneky I put a fresh mode executable built from this branch to /scratch/dave
If you could do some tests by running that, that'd be what I'm hoping for. (recommended tests above).

That plus look at the documentation changes.

I'd leave it to @JohnHalleyGotway to look at code changes.

[JohnHalleyGotway]

I approve of these changes... with a couple minor proposed fixes to spacing and capitalization.

I note that all the GHA tests all ran and flagged no diffs. I reviewed the code changes, was able to step through the logic described in the comments, and think it makes sense. I also see that MODE is now making use of the default MODEMultivarConfig_default file that already existed but wasn't ever being read. Thanks for updating the user's guide to reference that config file.

The User's Guide could be updated to specifically outline this logic for how the merge_flag and merge_thresh config options are parsed. But I suspect that's too much detail for the User's Guide. If @hertneky sees it differently and would like this logic described there, then I defer to her.

Thanks for getting this one across the finish line @davidalbo!

[JohnHalleyGotway]

Suggested change

	} else {
	} else {

Minor point. Just aligning braces.

[JohnHalleyGotway]

Suggested change

	// becAuse that is inconsistent
	// because that is inconsistent

[hertneky]

Test cntrl run with merge flag=THRESH and thresholds specified for the various fields. -> Object for fcst/obs look okay, all objects are merged into 1 cluster for both fcst/obs.

Test not specifying merge_flag/merge_thresh and make sure it defaults to NONE. -> Defaults to None and uses >=3.5 for all vars. Not sure why it specifies a random value for thresh, when merge is set to None, but it doesn't matter I suppose, since it is not used. Objects look the same as cntrl and no merging/clustered objects as expected.

Test specifying merge_flag=THRESH but no merge_thresh and observe the error exit. -> Errors as expected - need to specify a threshold.

Test usage of merge_thresh but no merge_flag and observe the error exit. -> Errors as expected - need to specify merge_flag