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# how to calculate a serie of a function with two variables

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hi everybody. i want to calculate the sum of a serie that has a function which has two variables named 'xi' and 'eta'. 'xi' and 'eta' are the coordinates of 4 points. for example i want to calculate the sum of the serie from point 1 to point 4 and in each point 'xi' and 'eta' has a specific value. can anyone help me how to write the code??
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### Answers (4)

dpb on 22 Feb 2015
xi=[list of four values];
eta=[list of four more presumably different values];
func=yourfunction(xi,eta); % compute the function
sumFunc=cumsum(func);
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dpb on 22 Feb 2015
How do we Know that? You didn't show any more of your work than your original question... :(

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Shoaibur Rahman on 22 Feb 2015
% xi eta
x =[1 2;...
3 4;...
4 5;...
6 7];
y = sum(x) % only sum of all elements along each column
y = cumsum(x) % cumulative sum along each column
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Image Analyst on 22 Feb 2015
Be more specific. Why can't you give us the series? Is it homework or something? If you don't get more specific then you'll just get more answers like dpb's (which is all your fault rather than dpb's because you were not specific enough to be able to answer your question).
What's wrong with using the sum() function, or even a brute force for loop()?
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Image Analyst on 22 Feb 2015
If you want to sum a 3D matrix "j" between certain rows and columns, do this
subArray = j(row1:row2, col1:col2, :);
theSum = sum(subArray(:));

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Omidreza Ghafarinejad on 24 Feb 2015
thanks people for your responces. i solved the problem. i used "subs" to assign values to my two variables in a loop.
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