PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

Fourier and Laplace 417

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MATLAB Solution

% Script file : analysis _ RLC

t =-1:0.1:8;t0=0;

u = stepfun(t,t0);

it = 50/3*exp(-t).*sin(3*t).*u;

subplot(2,1,1)

plot(t,it);

title(‘i(t) vs t (numeric solution)’)

xlabel(‘time(sec)’)

ylabel(‘Amplitude (amps)’)

axis([0 6 -4 11])

syms s zs

zs = 2+s+(1/(s*.1));

vs = 50/s;

ILs = vs/zs;

IL = ilaplace(ILs);

disp(‘*******************************************’)

disp(‘ **** symbolic result (sw closes at t=0)*****’)

disp(‘The current i(t) (in amps) is :’)

simIL = simplify(IL);

disp(simIL)

subplot(2,1,2)

ezplot(simIL)

title(‘i(t) vs. t (symbolic solution)’)

axis([0 6 -4 11])

xlabel(‘time(sec)’)

ylabel(‘Amplitude (amps)’)

t0=1;

IL = ilaplace((ILs)*exp(-s)); %sw closes at t=1

disp(‘******* *symbolic result(sw closes at t=1) *****’)

disp(‘The current i(t) (in amps) is given by :’)

simIL = simplify(IL);

disp(simIL)

disp(‘***************************************’)