function [cost,d_model]=cost_beam(CK,time,disp)
x0 = [disp(1) 0];
C = CK(1);
K = CK(2);
[t,x] = ode23(@ode_model, time, x0, [], C, K);
d_model = x(:,1);
cost = sum((d_model-disp).^2);