Exceeds array bounds Error when running m-file, but no problem if the function is run alone.

Hello, I m new at Matlab and have a simple question:

I wrote a short m-file function with the purpose of showing me the exact index where 3 conditions are fulfilled.

function[II]=cutdataB(VP,VT,PH)
global switchdata
II=find(switchdata(:,1)==VP&switchdata(:,3)==VT&switchdata(:,4)==PH-1)

If I run it, Matlab says:

cutdata (2,2,2)

Index in position 2 exceeds array bounds.

Error in cutdataB (line 3)

The confusing part is coming now:

Entering the third line alone, with filling in VP=2, VT=2, PH=2, results in Matlab showing the correct index vector

 II=find(switchdata(:,1)==2&switchdata(:,3)==2&switchdata(:,4)==2-1)

II =

    33

So, what is wrong with my m-file?

(If you re wondering, actually it's just a simplified version of another m file that I'm going to write. But in order to get that running, I m trying to at least manage to create an easy one)

Best regards

[Stephen23]

"So, what is wrong with my m-file?"

Global variables.

https://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/

https://www.mathworks.com/matlabcentral/answers/351423-problem-with-global-variables

https://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

etc.

Use one of the more reliable methods described in the MATLAB documentation:

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

Personally I find nested functions very intuitive and reliable.

Answer 1

[Ted Shultz]

I suspect your problem has to do with using different matrix named switchdata. Many people feel that is best to avoid using global variables if possible to avoid some of these types of confusion. Would it be possible to have the switchdata matrix passed to this function, rather than access it as a global?

[Stephen23]

"Many people feel that is best to avoid using global variables..."

Including the MATLAB documentation, which clearly states: "Use global variables sparingly, if at all" and recommends better ways of passing data between workspaces.

https://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html