"Assignment has more non-singleton rhs dimensions than non-singleton subscripts" help please!

def(i,j,m) = F_Co / k(i,j,m); is where I am getting the error, but it seems like I'm multiplying a singleton by a singleton. What is wrong?

    G = 11.5E6;
    d = 0.01 : 0.001 : 0.1;
    D = 0.1 : 0.01 : 1;  
    N = 1 : .1 : 10;

    A = length(d);
    B = length(D);
    E = length(N);

    C   = zeros(A,B);
    K_s = zeros(A,B);
    K_w = zeros(A,B);
    k   = zeros(A,B,E);
    def = zeros(A,B,E);

    for i = 1:A     

        for j = 1:B              
            C(i,j) = D(j) / d(i);                   
            K_s(i,j) = 1 + (0.5 ./ C(i,j));                    
            K_w(i,j) = (4 .* C(i,j) - 1)./(4 .* C(i,j) - 4)+(0.615 ./ C(i,j));     
            for m = 1:E
                k(i,j,m) = (d(i) .* G)./(8 .* N(m) .* C(i,j).^3);
                def(i,j,m) = F_Co / k(i,j,m);
            end
        end
    end

[Star Strider]

What is ‘F_Co’?

Is it a scalar?