function [xx,vv,tt]=vtb4_2(M,K,x0,v0,tf,plotpar)%VTB4_2 Free response of an undamped system.% [x,v,t]=VTB4_2(M,K,x0,v0,tf) will return the displacement (x) and% velocity (v) response for the system described by the mass% matrix M and stiffness matrix K.  The vector of time points, t,% is also returned.  The initial displacement, x0, and initial % velocity, v0, must also be a column vector input into the % function. The response is plotted from zero to final time tf.% [x,v,t]=VTB4_2(M,K,x0,v0,tf,plotpar) will also plot the various % responses depending on the value of plotpar:%% plotpar = 1: plot only displacements (x)% plotpar = 2: plot only velocities (v)% plotpar = 3: plot both displacements and velocitiesclg__gnuplot_set__ nokeyif nargin == 5  plotpar=0;endif plotpar~=0  aa=version;ll=length(aa);endplotpart=0:tf/200:tf;N=length(M);A=[zeros(N) eye(N);-M\K zeros(N)];B=zeros(2*N,1);IC=[x0;v0];Ad=expm(A*(t(2)-t(1)));eig(Ad);X(:,1)=IC;for i=2:length(t)   X(:,i)=Ad*X(:,i-1);endx=X(1:N,:);v=X(N+1:2*N,:);%plotting routinesgrid('on')if plotpar~= 0   if plotpar~=2      for i=1:N        %plot(t,x(i,:))        ylabel(['Displacement of X',num2str(i)])        xlabel('time (sec)')        title('Press any key to continue')        plot(t,x(i,:))		pause      end   end    if plotpar~=1      for i=1:N        %plot(t,v(i,:))        ylabel(['Velocity of X',num2str(i)])        xlabel('time (sec)')        title('Press any key to continue')        plot(t,v(i,:))		pause      end   endendif nargout~=0xx=x;vv=v;tt=t;end