C0 = 1;
K0 = 1500;
CK0 = [C0;K0];
[CK2, cost2] = fminsearch(@cost2_beam, CK0, [], time, disp);  % cost2 is the SSE for WLS
C2 = CK2(1)
K2 = CK2(2)

[c, d_model2] =cost2_beam(CK2, time,disp);
d_res2 = disp - d_model2;
m = length(disp);
sigma22 = sum(d_res2.^2)/m;




figure
plot(time,disp,'--',time, d_model2,'r')
%set(gca, 'FontSize', 18);
legend('experimental data','model displacement')
title('Two-parameter model estimation');
xlabel('time (s)');
ylabel('displacement');
axis tight;
%axis([0 0.5 -0.00006 0.00006])


figure
plot(time,d_res2)
xlabel('time')
ylabel('residuals')
%axis tight;
axis([0 0.5 -0.00006 0.00006])


figure
plot(d_model2,d_res2,'g.')
xlabel('fitted')
ylabel('residuals')

figure
qqplot(d_res2)   
ylabel('residuals')