Refactor measurement and printing for future features

[phdum-a]

Refactoring of measurement and printing system in preparation for multi-excitation support.

• Separates outs measurements (to be done in PostOperator only) from printing (to be done by Solvers)
• Printing is now change from Postpro functions into small printer classes which also hold a table of results, rather than printing row-by-row. (This is where multi-excitations will add extra columns).
• The output path is now handled using std::filesystem more consistently
• Measurements in PostOperator are now cached so that printers don't have to worry about that the getter functions might trigger an expensive calculation or one that requires MPI communication.
• Add PALACE_MFEM_USE_EXCEPTIONS build flag for unit tests, since catch can't test for aborts.
• Other small tweaks and improvements

Note: The output of all solvers after these changes should be identical to the current output*, for easy testing. Changes which alter output will be in subsequent PRs.
[*With one trivial change in the logger for eigenvalues from \omega/2pi -> f]

[fedeinthemix]

Hi, since you are refactoring the output format to support multi-excitations, I'd like to ask if would consider adding an option to output S-parameter files in Touchstone format. It's a de-facto standard in circuit simulators and beyond.

[phdum-a]

Hi, since you are refactoring the output format to support multi-excitations, I'd like to ask if would consider adding an option to output S-parameter files in Touchstone format. It's a de-facto standard in circuit simulators and beyond.

Dear @fedeinthemix,

Thank you very much for your suggestion. We'll have to think about it more, but right now we don't have plans to print touchstone files directly in Palace.

In cases where people require touchstone files, we have recommended writing a script that reads in the palace csv files from all the separate simulations (e.g. using pandas) and then prints it in the right form. You could also look at scikit-rf that has a touchstone printer and parser.

For Palace, we do want a consistant file formats with other measurements not covered by touchstone, like energy or fields. Also the touchstone spec does not quite cover some cases, like simulating only a subset of columns of the s-matrix.

Please let use know, if there is there anything you think we are missing something in the Palace output. For example, is there something in the touchstone file format / metadata that you can't find easily?

Thanks!

[fedeinthemix]

Dear @phdum-a,

Thank you for your answer. I thought that an option to output Touchstone files would be convenient since most RF/mmW passive circuits simulated with palace will probably be used in circuit simulators. But, I understand point, and, as you say, writing a conversion procedure is not a big deal.

Thanks again for your answer.

[hughcars]

Generally looks pretty good. I have some changes I think need to be made at #325 from hughcars/new_postpro. Additionally given it's a large refactor, mention it in the CHANGELOG.md.

[phdum-a]

Rebased onto main

[hughcars]

Generally looks good to me. Caught some minor bugs, all my suggested changes are on hughcars/new_postpro #356. So feel free to merge that if you agree, then we're good to go.