How to make the sum of all elements?

Hi,

M=10;

I have a matrix M=mxn and I want the sum of all elements, for n and m from 1 to 10.

My question is why this:

for ii=1:M

for ij=1:M

A=sum(M(ii,ij));

end

end

does not give the same result as:

A= sum(M,'all');

Thanks in advance for your reply.

Answer 1

[madhan ravi]

The result is not the same because you are summing up a scalar in each iteration thats why example sum(5) ->5 so the one which you do after is the correct way to do that is sum(M,'all') which can also be written as sum(M(:)). Also ii should be from 1 to size(M,1) representing number of rows and ij from 1 to size(M,2) representing number of columns.

Example:

Code:

M=rand(3);  %your matrix
A=zeros(1,numel(M));  %preallocation
ctr=1;
for ii=1:size(M,1)
        for ij=1:size(M,2)
            A(ctr+1)=A(ctr)+(M(ii,ij));
            ctr=ctr+1;
        end
end
total_sum=max(A)
sum(M,'all') %if they are equal then the result obtained is correct

command window:

>> COMMUNITY
total_sum =
    4.8821
ans =
    4.8821
>>