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When I was studying for my undergraduate degree in EE, MATLAB required each function to be defined in its own file, even if it was a one-liner.

I'm studying for a graduate degree now, and I have to write a project in MATLAB. Is this still a requirement for newer versions of MATLAB?

If it is possible to put more than one function in a file, are there any restrictions to this? For instance, can all the functions in the file be accessed from outside the file, or only the function that has the same name as the file?

Note: I am using MATLAB release R2007b.

The first function in an m-file (i.e. the main function), is invoked when that m-file is called. It is not required that the main function have the same name as the m-file, but for clarity it should. When the function and file name differ, the file name must be used to call the main function.

All subsequent functions in the m-file, called local functions (or "subfunctions" in the older terminology), can only be called by the main function and other local functions in that m-file. Functions in other m-files can not call them. Starting in R2016b, you can add local functions to scripts as well, although the scoping behavior is still the same (i.e. they can only be called from within the script).

In addition, you can also declare functions within other functions. These are called nested functions, and these can only be called from within the function they are nested. They can also have access to variables in functions in which they are nested, which makes them quite useful albeit slightly tricky to work with.

More food for thought...

There are some ways around the normal function scoping behavior outlined above, such as passing function handles as output arguments as mentioned in the answers from  (which, starting in R2013b, is facilitated by the localfunctions function). However, I wouldn't suggest making it a habit of resorting to such tricks, as there are likely much better options for organizing your functions and files.

For example, let's say you have a main function A in an m-file A.m, along with local functions DE, and F. Now let's say you have two other related functions B and C in m-files B.m and C.m, respectively, that you also want to be able to call DE, and F. Here are some options you have:

  • Put DE, and F each in their own separate m-files, allowing any other function to call them. The downside is that the scope of these functions is large and isn't restricted to just AB, and C, but the upside is that this is quite simple.

  • Create a defineMyFunctions m-file (like in Jonas' example) with DE, and F as local functions and a main function that simply returns function handles to them. This allows you to keep DE, and F in the same file, but it doesn't do anything regarding the scope of these functions since any function that can call defineMyFunctions can invoke them. You also then have to worry about passing the function handles around as arguments to make sure you have them where you need them.

  • Copy DE and F into B.m and C.m as local functions. This limits the scope of their usage to just AB, and C, but makes updating and maintenance of your code a nightmare because you have three copies of the same code in different places.

  • Use private functions! If you have AB, and C in the same directory, you can create a subdirectory called private and place DE, and F in there, each as a separate m-file. This limits their scope so they can only be called by functions in the directory immediately above (i.e. AB, and C) and keeps them together in the same place (but still different m-files):

    myDirectory/
        A.m
        B.m
        C.m
        private/
            D.m
            E.m
            F.m

All this goes somewhat outside the scope of your question, and is probably more detail than you need, but I thought it might be good to touch upon the more general concern of organizing all of your m-files. ;)

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