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Adding values of Columns in a matrix to create another matrix (for loop)

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Anna B
Anna B on 19 Dec 2019
Commented: Ridwan Alam on 20 Dec 2019
I have a 442x25 matrix 'yield' which I want to sum each column in 'yield' to create a 1x25 matrix 'nyi', so this can be multiplied by another 1x25 matrix Np.
I ran this exact code earlier on a different computer where both of the matrices were produced the size they are meant to be so i am not sure what is wrong.
It seems as if the code thinks there are only two columns.? But I have 25 columns
I am an amateur when it comes to matlab so I would really appreciate any help!
See the code for my loop and errors produced:
dim=size(E_min,2);
fun = @(E) A*exp(-E/kT);
for i = 1:dim
Np=integral(fun,E_min(i), E_max(i));
Np(i)=Np;
y=yield(:,1:i,1);
nyi=sum(y);
num(:,i)=nyi*Np(i);
end
The code is recognising my dim as 1x25 (which is correct) however when I run the following loop I am getting an error
Unable to perform assignment because the size of the left side is 1-by-1 and
the size of the right side is 1-by-2
Error in matrixfunction (line 41)
num(:,i)=nyi*Np(i);

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Accepted Answer

Ridwan Alam
Ridwan Alam on 19 Dec 2019
Edited: Ridwan Alam on 19 Dec 2019
dim=size(E_min,2);
% dim = 25
fun = @(E) A*exp(-E/kT);
Np = [];
nyi = [];
for i = 1:dim
Np(i)=integral(fun,E_min(i), E_max(i));
% size(Np) is 1x25
% size(yield) is 442 x 25
y=yield(:,i); % size(y) is 442 x 1
nyi(i)=sum(y); % size(nyi) is 1x25
end
num = nyi .* Np; % size(num) is 1x25
Hope this helps!

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More Answers (1)

Allen
Allen on 19 Dec 2019
Anna, if you are trying to multiple two 1x25 vectors element-wise then try using a period in front of the multiplication operator.
% Two 1x25 vectors with random values
Np = rand([1,25]);
nyi = rand([1,25]);
% Use '.*' for element-wise calculations instead of '*' which is trying to perform dot-multiplication.
% For '*' to work with two vectors they would need to be sized 1xn and nx1.
Np.*nyi

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