Is it possible to define more than one function pe

问题:

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.

回答1:

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 SCFrench and Jonas (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 D, E, 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 D, E, and F. Here are some options you have:

• Put D, E, 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 A, B, and C, but the upside is that this is quite simple.

• Create a defineMyFunctions m-file (like in Jonas\' example) with D, E, and F as local functions and a main function that simply returns function handles to them. This allows you to keep D, E, 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 D, E and F into B.m and C.m as local functions. This limits the scope of their usage to just A, B, 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 A, B, and C in the same directory, you can create a subdirectory called private and place D, E, 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. A, B, 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. ;)

回答2:

Generally, the answer to your question is no, you cannot define more than one externally visible function per file. You can return function handles to local functions, though, and a convenient way to do so is to make them fields of a struct. Here is an example:

function funs = makefuns
  funs.fun1=@fun1;
  funs.fun2=@fun2;
end

function y=fun1(x)
  y=x;
end

function z=fun2
  z=1;
end

And here is how it could be used:

>> myfuns = makefuns;
>> myfuns.fun1(5)    
ans =
     5
>> myfuns.fun2()     
ans =
     1

回答3:

The only way to have multiple, separately accessible functions in a single file is to define STATIC METHODS using object-oriented programming. You\'d access the function as myClass.static1(), myClass.static2() etc.

OOP functionality is only officially supported since R2008a, so unless you want to use the old, undocumented OOP syntax, the answer for you is no, as explained by @gnovice.

EDIT

One more way to define multiple functions inside a file that are accessible from the outside is to create a function that returns multiple function handles. In other words, you\'d call your defining function as [fun1,fun2,fun3]=defineMyFunctions, after which you could use out1=fun1(inputs) etc.

回答4:

I really like SCFrench\'s answer - I would like to point out that it can easily be modified to import the functions directly to the workspace using the assignin function. (Doing it like this reminds me a lot of Python\'s \"import x from y\" way of doing things)

function message = makefuns
  assignin(\'base\',\'fun1\',@fun1);
  assignin(\'base\',\'fun2\',@fun2);
  message=\'Done importing functions to workspace\';
end

function y=fun1(x)
  y=x;
end

function z=fun2
  z=1;
end

And then used thusly:

>> makefuns
ans =
Done importing functions to workspace

>> fun1(123)
ans =
   123

>> fun2()
ans =
     1

回答5:

Along the same lines as SCFrench\'s answer, but with a more C# style spin..

I would (and often do) make a class containing multiple static methods. For example:

classdef Statistics

    methods(Static)
        function val = MyMean(data)
            val = mean(data);
        end

        function val = MyStd(data)
            val = std(data);
        end
    end

end

As the methods are static you don\'t need to instansiate the class. You call the functions as follows:

data = 1:10;

mean = Statistics.MyMean(data);
std = Statistics.MyStd(data);     

回答6:

I define multiple functions in one .m file with Octave and then use the command from within the .m file where I need to make use of the functions from that file:

source(\"mycode.m\");

Not sure if this is available with Matlab.

octave:8> help source
\'source\' is a built-in function

 -- Built-in Function:  source (FILE)
     Parse and execute the contents of FILE.  This is equivalent to
     executing commands from a script file, but without requiring the
     file to be named `FILE.m\'.

回答7:

You could also group functions in one main file together with the main function looking like this:

function [varargout] = main( subfun, varargin )
[varargout{1:nargout}] = feval( subfun, varargin{:} ); 

% paste your subfunctions below ....
function str=subfun1
str=\'hello\'

Then calling subfun1 would look like this: str=main(\'subfun1\')

回答8:

As of R2017b, this is not officially possible. The relevant documentation states that:

Program files can contain multiple functions. If the file contains only function definitions, the first function is the main function, and is the function that MATLAB associates with the file name. Functions that follow the main function or script code are called local functions. Local functions are only available within the file.

However, workarounds suggested in other answers can achieve something similar.

回答9:

I have try with the SCFRench and with the Ru Hasha on octave.

And finally it works: but I have done some modification

function message = makefuns
    assignin(\'base\',\'fun1\', @fun1);   % Ru Hasha
    assignin(\'base\', \'fun2\', @fun2);  % Ru Hasha
    message.fun1=@fun1;               % SCFrench
    message.fun2=@fun2;               % SCFrench
end

function y=fun1(x)
    y=x;
end

function z=fun2
    z=1;
end

Can be called in other \'m\' file:

printf(\"%d\\n\", makefuns.fun1(123));
printf(\"%d\\n\", makefuns.fun2());

update:

I added an answer because neither the +72 nor the +20 worked in octave for me. The one I wrote works perfectly (and I tested it last Friday when I later wrote the post).