I'm excited to see what you will do with this!
I think you are right, that FloatMatrix.cpp is missing in the sources list, and I'm afraid this is still the case with current
develop branch. I'll fix it up in a PR and deploy to the website to test, I'll just have to take care of some other changes first.
And yes, the website has had
develop or even feature branches deployed lately, in order to roll out and test new features a bit faster.
Finally regarding Cortex optimisations, it's true there's no NEON support but the cores have some SIMD features, so that 16-bit and 8-bit data can be processed 2 or 4 at a time. The CMSIS libs (which we take advantage of e.g. in the FloatArray and FloatMatrix classes) leverage this, but for floats SIMD doesn't make any difference. However we still find the optimised functions tend to run a bit faster, probably thanks to loop unwinding and making the most of the many float registers. Other functions like sin, cos and FFTs use table lookups, and they perform great regardless of data type.