xlswrite

Question

Nasir Qazi 2012-3-23

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https://ww2.mathworks.cn/matlabcentral/answers/33231-xlswrite

I have a Program where a values of 'A' is changing in each iteration and I want to save each value separately in excel so later I can make a graph, I am using xlswrite but it overwrite the previous value which I don't want them to change , how can I do that ..

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Answer 1

Ken Atwell 2012-3-23

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Hi Nasir,

Is the value of A a scalar? Even if you could make this work, writing to an Excel file at every loop iteration sounds like slow going. How about preserving the values of A within MATLAB itself:

 allA = zeros(numLoopIterations, 1);
 for i=1:numLoopIterations
   A = ...
   allA(i) = A;
 end
 plot(allA)

I've pre-allocated above for performance reasons, but I suspect even not pre-allocating (if numLoopIternations is not known, for example) will be much faster than writing to Excel:

 allA = [];
 while ...
   A = ...
   allA(end+1) = A;
 end
 plot(allA)

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Cynthia 2012-4-4

This answer was very helpful, but how do you do this if A is a vector, not a scalar? I'm not plotting the data but I'm exporting it into MS Excel. The last iteration keeps getting written over just like Nasir's plot was written over.

Ken Atwell 2012-4-4

In the vector case, if A is always the same length, it is only incrementally more complicated. You can create a 2-D matrix, with each row representing one "column" of A:

allA = zeros(numLoopIterations, lengthOfVectorfA);

for i=1:numLoopIterations

A = ...

allA(i,:) = A;

end

If A is not the same length in each iteration (i.e., your matrix/spreadsheet will be ragged right), you will need to use a cell array or some such to record vectors of varying lengths. Is this the case for you, Cynthia?

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