MATLAB error: Undefined function or method X for i

问题:

This question already has an answer here:

• “Undefined function 'function_name' for input arguments of type 'double'.” 2 answers

I'm a new user of Matlab, can you please help:
I have the following code in an .M file:

function f = divrat(w, C)
S=sqrt(diag(diag(C)));
s=diag(S);
f=sqrt(w'*C*w)/(w'*s);

I have stored this file (divrat.M) in the normal Matlab path, and therefore I'm assuming that Matlab will read the function when it's starting and that this function therefore should be available to use.

However, when I type

>> divrat(w, C)

I get the following error

??? Undefined function or method 'divrat' for input arguments of type 'double'.

What is the error message telling me to do, I can't see any error in the code or the function call?

回答1:

You get this error when the function isn't on the MATLAB path or in pwd.

First, make sure that you are able to find the function using:

>> which divrat
c:\work\divrat\divrat.m

If it returns:

>> which divrat
'divrat' not found.

It is not on the MATLAB path or in PWD.

Second, make sure that the directory that contains divrat is on the MATLAB path using the PATH command. It may be that a directory that you thought was on the path isn't actually on the path.

Finally, make sure you aren't using a "private" directory. If divrat is in a directory named private, it will be accessible by functions in the parent directory, but not from the MATLAB command line:

>> foo

ans =

     1

>> divrat(1,1)
??? Undefined function or method 'divrat' for input arguments of type 'double'.

>> which -all divrat
c:\work\divrat\private\divrat.m  % Private to divrat

回答2:

As others have pointed out, this is very probably a problem with the path of the function file not being in Matlab's 'path'.

One easy way to verify this is to open your function in the Editor and press the F5 key. This would make the Editor try to run the file, and in case the file is not in path, it will prompt you with a message box. Choose Add to Path in that, and you must be fine to go.

One side note: at the end of the above process, Matlab command window will give an error saying arguments missing: obviously, we didn't provide any arguments when we tried to run from the editor. But from now on you can use the function from the command line giving the correct arguments.

回答3:

The most common cause of this problem is that Matlab cannot find the file on it's search path. Basically, Matlab looks for files in:

1. The current directory (pwd);
2. Directly in a directory on the path (to see the path, type path at the command line)
3. In a directory named @(whatever the class of the first argument is) that is in any directory above.
   
   

   As someone else suggested, you can use the command which, but that is often unhelpful in this case - it tells you Matlab can't find the file, which you knew already.
   
   So the first thing to do is make sure the file is locatable on the path.
   

   Next thing to do is make sure that the file that matlab is finding (use which) requires the same type as the first argument you are actually passing. I.el, If w is supposed to be different class, and there is a divrat function there, but w is actually empty, [], so matlab is looking for Double/divrat, when there is only a @(yourclass)/divrat. This is just speculation on my part, but this often bites me.

回答4:

The function itself is valid matlab-code. The problem must be something else.
Try calling the function from within the directory it is located or add that directory to your searchpath using addpath('pathname').

回答5:

The error code indicates the function definition cannot be found. Make sure you're calling the function from the same workspace as the divrat.m file is stored. And make sure divrat function is not a subfunction, it should be first function declaration in the file. You can also try to call the function from the same divrat.m file in order to see if the problem is with workspace selection or the function.

By the way, why didn't you simply say

s = sqrt(diag(C));

Wouldn't it be the same?

回答6:

Also, name it divrat.m, not divrat.M. This shouldn't matter on most OSes, but who knows...

You can also test whether matlab can find a function by using the which command, i.e.

which divrat

回答7:

I am pretty sure that the reason why this problem happened is because of the license of the toolbox (package) in which this function belongs in. Write which divrat and see what will be the result. If it returns path of the function and the comment Has no license available, then the problem is related to the license. That means, license of the package is not set correctly. Mostly it happens if the package (toolbox) of this function is added later, i.e., after installation of the original matlab. Please check and solve the license issue, then it will work fine.