%-------------------------------------
%Homework 4
%Greenwood Problem 4.2
%Henry Lam
%-------------------------------------

global A1 A2
%Given value of circuit elements
L=0.12; %Henry
C=32e-6; %Farads
R=92;   %Ohm

t0=0; %define the initial time
tf=15e-3;  %define the final time
nsteps=500;  %number of steps from t0 to tf)
hsteps=(tf-t0)/nsteps;
tspan=t0:hsteps:tf;

A1=[0 -1/C;1/L 0]; %When only S1 is closed.
A2=[-1/(R*C) -1/C;1/L 0];  %When S2 is closed while S1 is already closed.

disp('Eigenvalue of A1 are:')
lambda1=eig(A1);
disp('Eigenvalue of A2 are:')
lambda2=eig(A2);

x0=[40e3 0.0];  % initial conditions
[t,x]=ode23('hw4_gw42',tspan,x0);

subplot(2,1,1)
plot(t,x(:,1),'Linewidth',1.5), grid on
title('When S1 is closed, S2 is open');
xlabel('time(sec)')
ylabel('Vc(Volts)')

subplot(2,1,2)
plot(t,x(:,2),'Linewidth',1.5), grid on
title('When S1 and S2 are closed');
xlabel('time(sec)')
ylabel('iL(amps)')
The switch S1 closed first then 5ms later switch S2 close
function xdot=hw4_gw42(t,x)
global A1 A2
%state variables;
%x(1)=Vc, x(2)=iL
xdot=zeros(2,1);
if(t<5e-3)
    xdot=A1*x;  %state space equation when S1 is closed.
else
    xdot=A2*x;  %state space equation when S1 and S2 are closed.
End