This is impossible to answer. There are many, many thousands of "algorithms" in the various calculations in MATLAB, as there are a huge number of functions, especially when you add in the toolboxes.
So the only possible answer to your question is that you need to:
- Read the documentation for the code in question. Understand what it is attempting to do. Then you may need to do some research on that particular problem, to understand why some specific algorithm was chosen.
- Probably take at least a basic course in numerical analysis.
Your question may be as simple as to how arithmetic works in a floating point environment. So you may need to start there. We cannot know, since your question is unimaginably broad.
If you have a specific question, about a specific problem, then ask it.
