MATLAB: Keep getting this error and I cannot figure out why: Dimensions of arrays being concatenated are not consistent.

differential equat...differential equationsloop ode45MATLABode45

I have the following code trying to solve differential equation of second order:
[t,X] = ode45(@(t,X) odefun_4(t,X,u), [0 10], [0;0]);
function dx = odefun_4(t,x,u)
    %xdisp(u);
    m = 15;
    b = 0.2;
    k = 2;
    %u = interp1(ut,u,t);
    dx = [x(2); u/m - (b/m)*x(2) - (k/m)*x(1)];
end
Vector u is a 1×100 vector. I expect to get a 2×100 matrix as the return value. What am I doing wrong ?

Best Answer

EDITED
m = 15;
b = 0.2;
k = 2;
ut = linspace(0, 10);
u = 5 * sin(2 * ut) + 10.5; % input of our system - external forc
dx = @(t,x,u)[x(2); u/m - (b/m)*x(2) - (k/m)*x(1)]
for u=u
[t,X] = ode45(@(t,x)dx(t,x,u), [0 10], [0;0]); %function calling
plot(t,X)     
hold on
end
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