Adds an additional test reference for model level index ObsFunction

[mikecooke77]

Description

This PR updates the model_level_index_obs.nc4 test file so that it contains one additional test reference array to allow for an update to the ufo_function_modellevelindex ctest in ufo.

Issue(s) addressed

Resolves ufo#4160

Dependencies

To be merged with the following associated PRs:

• https://github.com/JCSDA-internal/ufo/pull/4161
• https://github.com/JCSDA-internal/jedi-docs/pull/1038

Impact

None as the default behaviour is unchanged.

Checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have run the unit tests before creating the PR

[ReubenHill]

So which way does the rounding go with this new test reference? If I have something exactly between levels 1 and 2, does it round to 1 or to 2?

[mikecooke77]

So which way does the rounding go with this new test reference? If I have something exactly between levels 1 and 2, does it round to 1 or to 2?

Its the same as the previous function i.e. 1.5 becomes level 1 because the weight has to be greater than 0.5 for it to have the additional one added.

[ReubenHill]

So which way does the rounding go with this new test reference? If I have something exactly between levels 1 and 2, does it round to 1 or to 2?

Its the same as the previous function i.e. 1.5 becomes level 1 because the weight has to be greater than 0.5 for it to have the additional one added.

Is that not the reverse of what one might expect? I.e. 1.5 would conventionally round to 2.

[mikecooke77]

So which way does the rounding go with this new test reference? If I have something exactly between levels 1 and 2, does it round to 1 or to 2?

Its the same as the previous function i.e. 1.5 becomes level 1 because the weight has to be greater than 0.5 for it to have the additional one added.

Is that not the reverse of what one might expect? I.e. 1.5 would conventionally round to 2.

Yes I agree. I did it like this to match the previously approved function which had to use a less than rather than a less than or equals too. In practise for GNSSRO it made no difference to the output.

@ctgh and @ReubenHill do you both agree it should round up? If so I will change.

[ctgh]

That sounds good to me, thanks.

[mikecooke77]

OK changed in this datafile and the ufo pr