# eigen values (principle stresses) of large date

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fadzhi on 24 Aug 2016
Answered: Farouk Moukaddem on 26 Aug 2016
Hi all, I need to calculate the eigenvalues(principle stresses). My data is based on time and for each time interval, i have 9 components (3x3 matrix). I am not familiar with matlab but i learned that i can calculate the eigenvalue with a simple eig() command. So in this case, how can use this command (will it require a for loop) so that in the end, i am able to plot the time vs. eigen values. (3 values). Will appreciate any ideas or suggestion?

Farouk Moukaddem on 26 Aug 2016
You can use a for-loop and the "eig" function to find the eigenvalues of the three matrices you have, by grouping the matrices into a cell array and iterating over it.
Refer to the following example:
A=[1 2;3 4],
B=[5 6;7 8];
C=[9 10;11 12];
D={A,B,C}; % Creating the cell array
for i=1:3
eig(D{i})
end
Refer to the following documentation link for more information about the "eig" function: http://www.mathworks.com/help/matlab/ref/eig.html
Best,
Farouk

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