x=[2 1 0 0
0 1 1 1
0 1 1 1
1 0 3 1]
numNonZeros = nnz(x)
Not sure what you want for the second question since your sum does not include all 16 elements.
x2=x;
x2(x==0) = 1
s = sum(1./x2(:))
% Sum 11 of the 16 -- only some of them for some reason.
% Not sure which to take and which to exclude.
thesum = (1/2 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/3 + 1/1) % 11 of the 16
% Now sum all 16
thesum = (1/2 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/1 + 1/3 + 1/1)
If this is your homework, you're most likely not allowed to turn my code in as your own. And please tag it as homework if it is.
Regarding your edit, to sum up only elements where x is not zero:
x2=x(:); % Make a copy as a column vector.
x2(x==0) = [] % Remove the zeros.
s = sum(1./x2(:))
