how to plot function with a sine input in Matlab (not in simulink)

we just type command 'step(function)' to plot a function with input step but How to plot a function that use sine as an input in Matlab.

Answer 1

[Paulo Silva]

When you invoke the step function you are multiplying your function on the frequency domain by 1/s, the function you get from that operation is then converted to the time domain using the ilaplace function.

Now for you specific case you can first convert the function to the time domain using ilaplace and then multiply by sin(t).

For the plot make the t vector and use the plot function to plot the response

plot(t,f(t))

Example

syms s t 
TFC=evalc('tf([1 1],[1 1 1 0])') 
%subplot(211) 
[a b] = strread(TFC, '%s %s', 'delimiter',char(10)); 
num=sym(char(a(2))); 
den=sym(char(a(3))); 
tft=ilaplace(num/den); 
tt=0:0.01:10; 
plot(tt,subs(tft,t,tt).*sin(tt)) 
title('f*sin(t)') %response to input sin(t) 
ylabel('Amplitude') 
xlabel('time')

[Geraint Bevan]

The answer above is completely wrong.

Multiplying the inverse Laplace transform by a sine wave is not at all equivalent to applying a sine input to the system.

If you wish to use ilaplace to do this, you should apply the sine input in the 's' domain and then transform back into the time domain.

e.g.

syms s

G = 1/(1+s)

U = 4/(s^2+16) % sin(4t)

Y = G*U

y = ilaplace(Y)

Answer 2

[Geraint Bevan]

Use the lsim function to apply an arbitrary input to a system.

G = tf(1,[1,1])

t = [0:0.01:10]

u = sin(t)

[y,t] = lsim(G,u,t)

plot(t,u,t,y)

legend('Input','Output')