How to check "Undefined function or variable..." error with a variable in Matlab program?

I have code as follows:

for i=1:3
   M=Mtmp(i)+(Mtmp(i+1)-Mtmp(i))*(t-t(i))/(t(i+1)-t(i));
end

And, Mtmp(i) and t(i) are two arrays which are defined in previous code snippet.

I run that code and receive an error: Undefined function or variable 'M'

I think, in Matlab, we can use a variable that we do not have to declare one, why do I receive that error? Thanks.

Answer 1

[Azzi Abdelmalek]

I am sure the error does not concern those lines of code. Post the entire code, maybe there is another line where M is used at the right of your expression.

[Azzi Abdelmalek]

[Tuoi commented]

Hi Azzi, I try to display the value of M by disp() function, I put the command line:

disp(['M= ',num2str(M)]);
after the above code (my post 1#), and run it, it generate that error (at disp() function). I hope you help me. Thanks.

[Azzi Abdelmalek]

If M is defined, your code is correct. For example:

M=[1 2 3]
disp(['M= ',num2str(M)]);

Check If M is defined by typing M in Matlab command Windows