Read complex values from `.mat` files via HDF5 C++ API

[willGraham01]

Allows us to read complex MATLAB arrays via the HDF5 API.

To do this, we have to define (at runtime) a H5::CompType instance that describes the data-structure that needs to be read in - in this case, that describes the format in which MATLAB saves complex data. Note that there is no HDF5 standard for complex datatypes, so trying to read complex data from something like h5py- created files will require separate, but similar, treatment.

• Concerns #285 | We can now read in complex data from .mat input files

Implementation

The hdf5_compound_types.{h,cpp} file has been created to contain compound types.

Currently there is only one compound type, MATLAB_complex. But the following convention has been set given the remark above about compound datatypes and the lack of standard format for complex-values in particular:

• Each compound type has it's own namespace within this file
• Each namespace contains:
  • The struct that is compatible with the compound data-type to be read
  • A to_hdf5_CompType() method that returns a H5::CompType instance, that can be passed to the API to read data into the aforementioned struct via the read method.
  • Any number of helpful converter functions to std:: datatypes (or std::vectors thereof) so that we don't have to reimplement algebra.

Testing

Additional tests in test_hdf5_compound_types.cpp that check that:

• The new overload of the HDF5Reader::read() method performs as expected for MATLAB_complex types
• The other supporting functions in the namespace perform correctly.

[codecov[bot]]

Codecov Report

Patch coverage: 63% and project coverage change: -1 :warning:

Comparison is base (e8e9809) 27% compared to head (221a033) 26%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #343 +/- ## =================================== - Coverage 27% 26% -1% =================================== Files 77 83 +6 Lines 3687 3687 =================================== - Hits 978 949 -29 - Misses 2709 2738 +29 ``` | [Impacted Files](https://app.codecov.io/gh/UCL/TDMS/pull/343?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL) | Coverage Δ | | |---|---|---| | [tdms/include/hdf5\_io/hdf5\_compound\_types.h](https://app.codecov.io/gh/UCL/TDMS/pull/343?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL#diff-dGRtcy9pbmNsdWRlL2hkZjVfaW8vaGRmNV9jb21wb3VuZF90eXBlcy5o) | `0% <0%> (ø)` | | | [tdms/include/hdf5\_io/hdf5\_reader.h](https://app.codecov.io/gh/UCL/TDMS/pull/343?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL#diff-dGRtcy9pbmNsdWRlL2hkZjVfaW8vaGRmNV9yZWFkZXIuaA==) | `0% <0%> (ø)` | | | [tdms/src/hdf5\_io/hdf5\_compound\_types.cpp](https://app.codecov.io/gh/UCL/TDMS/pull/343?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL#diff-dGRtcy9zcmMvaGRmNV9pby9oZGY1X2NvbXBvdW5kX3R5cGVzLmNwcA==) | `86% <86%> (ø)` | | ... and [20 files with indirect coverage changes](https://app.codecov.io/gh/UCL/TDMS/pull/343/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL)

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[samcunliffe]

Nice!