i have Question about Inverse lapalce transform & plot

hi. i try to cording matlab to draw a graph of inverse laplace transofrm result

F is a function made of R and G. and i want to inverse laplace transform that function F and draw a graph.

i really try hard but it didn't work. maybe there is a error at plot cording.

can i get a advice about it?

thank you.

here's my cording.

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syms s

R = 1/s

G = 75/(s)^2+10.25*s+100.65

F = R * G

a = ilaplace (F)

x = t

t = [0,0.01,10];

y = a;

plot(x,y)

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[Paul]

Are you sure you don't mean:

G = 75/( s^2+10.25*s+100.65 )

[jongil park]

oh yes, that is right. i did mistake about this. thank you :D

Answer 1

[Star Strider]

Try this —

syms s
R = 1/s

R = 

G = 75/(s)^2+10.25*s+100.65

G = 

F = R * G

F = 

a = ilaplace (F)

a = 

% x = t
t = [0 10];
y = a;
fplot(y,t)
grid

Use fplot, not plot, for symbollic plots.

.

[Paul]

It's unfortunate that fplot() isn't smart enough to indicate the delta(t) at t = 0.

[Star Strider]

It does, actually.

It indicates a singularity at 0 (with a suitably high resolution). That’s likely the best it can do.

syms s 

f = ilaplace(41*s/(4*s))

f = 

figure
fplot(f, [-1 1]*1E-500)
ylim([-1 1]*50)

.

[jongil park]

thank you. problem was "plot" fucntion. XDD

[Paul]

Interesting. I tried a couple of other cases and that vertical dashed line only shows up when fplotting over a very small range as you did. I don't see why one should have to fplot over only microscopically small segments where one can't see the rest of the plot. I thought that vertical dashed line is used by fplot to indicate a singularity. I don't think delta(t) should be demarcated as a singularity, but I guess that may be arguable. However, other types of singularities show up on the plot without any special control of the x-limits

syms x real
fplot(1/x)

What I'd really like is for fplot() to show that delta(t) with an arrow, or something like that.

[Star Strider]

@jongil park — As always, my pleasure!

@Paul — If you consider this to be a bug, or would like this as an ‘enhancement’, you can report it as such, request the enhancement, or both. Perhaps having this as an option (such as 'ShowDeltaFunction','on') would work.