How to solve such a problem :Cannot perform the operation: {convex} .* {convex}

The variables are lioff and u, and u is a 2*20 column vector, and both sides are convex functions, so I don’t know how to multiply two convex functions. Thank you for your kind reply

for i=1:I
              for n=1:N
                  pioff(n,i)=o2*(2^(lioff(n,i)/(B*t0))-1)*(H^2+square_pos(norm(u(:,n)-si(:,i))))/y0;
              end
          end

You don’t (in CVX). That is non-convex.