# How to solve Index out of bounds because numel(A)=4

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Upasana Baishya on 12 Feb 2021
Commented: KSSV on 12 Feb 2021
My aim is to generate the intensity profile for the output light passing through a polariser and an analyser for different angles of analyser . I am cosidering a gaussian light beam.
gaussian function-
function H = my_gaussian(n, sigma)
two_sigma_sq = 2*sigma*sigma;
H = zeros(n);
for i = 1:n
for j = 1:n
x = i - n/2;
y = j - n/2;
H(i,j) = exp(-(x*x + y*y)/two_sigma_sq);
end
end
end
Intensity profile-
H = my_gaussian(256, 50) ;
Ph = 0; E1 = cosd(Ph); E2 = sind(Ph);
E = [E1 ; E2];
Th = [0 30 90];
for i = 1:length(Th)
A11 = cosd(Th(i))*cosd(Th(i));
A12 = cosd(Th(i))*sind(Th(i));
A21 = cosd(Th(i))*sind(Th(i));
A22 = sind(Th(i))*sind(Th(i));
A = [A11, A12; A21, A22]
O = A(i)*E
I = O'*O
IP = I*H;
figure, imshow(IP);axis image;colorbar;
end
I can put maximum 3 values of Th, it gives me correct answer but as soon as I put 4 values, the 4th value is Incorrect. If I try putting more than 4 values error comes up saying
" Attempted to access A(5); index out of bounds because numel(A)=4.
Error in Untitled2 (line 31)
O = A(i)*E "
What should I change in this program?
KSSV on 12 Feb 2021
What inputs you have tried? The given code now workd fine.

KSSV on 12 Feb 2021
This line:
O = A(i)*E ;
should be changed to:
O = A*E
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KSSV on 12 Feb 2021
Thanks is accepting/ voting the aswer.. :)