Getting errors on must return a coloumn vector

function dx=system(t2,x2)
global u;
dx(1,1)=x2(2)+u;
dx(2,1)=0;
[t2,x2]=ode45(@system, tspan,[0.005,0]);

Showing error in dx(1,1)=x2(2)+u;
as unable to perform assignment because left and right hand side are not compatible with sizes.

[KSSV]

Check the dimensions of u. It seems u is a vector and x2(2)+u is a vector which cannot be saved into a single element dx(1,1).