I've drifted away from the field, but last I heard Matlab is still a really big deal in digital signal processing and modeling RF signals and systems. There are e.g. toolchains to start with Matlab code and end up with a synthesized filter in an FPGA. Octave can be used as a stand-in for Matlab when you need to fiddle with some Matlab code but don't necessarily need the full-blown infrastructure of Matlab's "toolboxes", or when you're just learning the fundamentals of programming in a Matlab style. NumPy can fundamentally do the same stuff at this level, but the syntax for basic manipulation of vectors/matrices is significantly clunkier. This isn't a big deal when implementing a known solution, but for little REPL sketches and experimentation it's definitely been noticeable to me.