What type of entropy encoder does the MATLAB save() function use? I.e. how does that function work?

I am working on a compression project, and I used the default save() function in Matlab for the purpose of lossless (entropy) encoding. The transform module is all figured out.

I used the save() function to encode a 3d array that includes a bunch of zeros. I am sure that Matlab is using some kind of lossless compression with the save() function since, when I save that array, it ends up taking far less space than an array, say, containing no zeros at all. I had no success finding out what type of entropy encoding schemes are behind the function. Because it is a core part of the algorithm, I think I must at least know what is behind the function.

Plus, if you know any other type of entropy encoder that would do a better job in compressing a 3d array that contains zeros, I would really appreciate you sharing. Or, if you think I could easily write the code for that myself, then please let me know.

Answer 1

[Walter Roberson]

https://www.mathworks.com/matlabcentral/answers/93868-is-there-documentation-on-the-structure-of-mat-files-in-matlab#answer_103219

Look in the pdf, page 14. zlib is used. If I recall correctly, level 4 compression.