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

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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);

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!

Ridwan Alam on 19 Dec 2019
Anna B on 20 Dec 2019
This works perfect!! Thank you so much for your help!
Ridwan Alam on 20 Dec 2019

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