Undefined operator '+' for input arguments of type 'cell'

sum(k)={0};
for j=1:K
for i=1:K
    if(j~=i)
        sum(j)=(sum(j))+(f(i))
    end
end
end

[Walter Roberson]

Why are you initializing sum(k)={0}; instead of sum(k)=0 ? Are you expecting f(i) to return matrices of different sizes according to i? (If so then it is not clear what it would mean to add those.)

[Walter Roberson]

About 2 1/2 weeks from now, you are going to try to use the function sum and then get very confused by an error message about indices needing to be positive integers or logical.