Script not finding variable even when the variable is in my workspace

So I have a bunch of variables from a data file in my workspace and I'm making a script to plot a contour plot quickly and it works fine.

function contf(A,B,C)
a=min(A):(max(A)-min(A))/200:max(A);
b=min(B):(max(B)-min(B))/200:max(B);
[Aq,Bq]=meshgrid(a,b);
C=griddata(A,B,C,Aq,Bq);
contourf(Aq,Bq,C)
set(gca,'YDir','reverse');
set(gca,'xaxislocation','top');
end

However A and B are always X and Y, variables that are in my respectively in my workspace. When i try this shorter function its not working?

    function qcontf(C)
    A=X
    B=Y
    a=min(A):(max(A)-min(A))/200:max(A);
    b=min(B):(max(B)-min(B))/200:max(B);
    [Aq,Bq]=meshgrid(a,b);
    C=griddata(A,B,C,Aq,Bq);
    contourf(Aq,Bq,C)
    set(gca,'YDir','reverse');
    set(gca,'xaxislocation','top');
    end

I just get

Undefined function or variable 'X'.

Error in qcontf (line 2) A=X

Answer 1

[Thorsten]

The variables X and Y in your workspace are not known inside the function. You can use the following, but it's not considered good practice:

function qcontf(C)
global X
global Y

A=X
B=Y

[aaron Harvey]

Awesome thank-you! I guess its bad practice since the script will only work if you know what's inside it, but for the way im using it I don't mind. I'm trying to find an extra-lazy way to make almost 100 contour plots, all with the same X&Y.

[Thorsten]

But why don't you use the first version of your function with 3 arguments A, B, C and call it using

qcontf(X,Y,C)

[Stephen23]

@aaron Harvey: don't learn the bad practice of using globals when you can simply pass the values as arguments. Using globals is considered a bad practice in most programming languages, and passing arguments is what MATLAB recommends:

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

" Best Practice: Passing Arguments"

"The most secure way to extend the scope of a function variable is to use function input and output arguments, which allow you to pass values of variables."

Compare to this list:

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

and thousands of questions on this forum resulting from the decision to use globals.