function vtb3_1(m,c,k,Fo,tf,flag)%VTB3_1 Impulse response of a SDOF system.% VTB3_1(m,c,k,Fo,tf,1) plots the response of the system to an% impulse of magnitude Fo.  The input variables are the mass m,% the stiffness k, and the damping c.  The total time of the % response is tf.% VTB3_1(m,zeta,w,Fo,tf,2) plots the response of the system % described by the mass m, the damping ratio zeta, and the % undamped natural frequency w.    clcif flag == 1  num=Fo;  den=[m c k];else  zeta=c;  w=k;  num=Fo/m;  den=[1 2*zeta*w w^2];endt=0:tf/200:tf;x=step([num 0],den,t);plot(t,x)title('Impulse Response of the SDOF damped oscillator')ylabel('Displacement x(t)')xlabel('time  (sec)')