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

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aaron Harvey
aaron Harvey 2015-10-8
编辑： Stephen23 2015-10-8
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

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Thorsten
Thorsten 2015-10-8
编辑：Thorsten 2015-10-8
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
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Thorsten
Thorsten 2015-10-8
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
Stephen23 2015-10-8
编辑：Stephen23 2015-10-8
@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.

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