Discover MakerZone

MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi

Learn more

Discover what MATLAB® can do for your career.

Opportunities for recent engineering grads.

Apply Today

Thread Subject:
laplace function error?

Subject: laplace function error?

From: G

Date: 20 Sep, 2010 04:01:17

Message: 1 of 3

Hi All,
I am trying to do the laplace of a simple gaussian pulse. When I do the laplace, however, I do not get an answer. The answer just repeats the same equation in brackets just as below. I know the actual laplace/fourier of the gaussian pulse is the same as in the time domain. So is that what this is trying to tell me? If so, how do I begin using this in the laplace domain?

This was the code used and the answer:

syms t;
syms sig;
gau = exp(-0.5*(t.^2)*(1/(sig.^2)));
laplace(gau)
 
ans =
 
laplace(1/exp(t^2/(2*sig^2)), t, s)


Thanks.

Subject: laplace function error?

From: Nasser Abbasi

Date: 20 Sep, 2010 04:56:12

Message: 2 of 3

On Sep 19, 9:01 pm, "G " <geffglass...@hotmail.com> wrote:
> Hi All,
> I am trying to do the laplace of a simple gaussian pulse. When I do the laplace, however, I do not get an answer. The answer just repeats the same equation in brackets just as below. I know the actual laplace/fourier of the gaussian pulse is the same as in the time domain. So is that what this is trying to tell me? If so, how do I begin using this in the laplace domain?
>
> This was the code used and the answer:
>
> syms t;
> syms sig;
> gau = exp(-0.5*(t.^2)*(1/(sig.^2)));
> laplace(gau)
>
> ans =
>
> laplace(1/exp(t^2/(2*sig^2)), t, s)
>
> Thanks.


well, looks like Matlab just can't do this one.

fyi, here is the answer from Mathematica (I renamed your "sig"
variable as "y")

In[14]:= gau = Exp[ -1/2 * t^2/y^2 ];

LaplaceTransform[gau, t, s]

Out[15]=

E^((s^2 y^2)/2) Sqrt[Pi/2] y (-1+Sqrt[1/y^2] y+Erfc[(s y)/Sqrt[2]])

ps. why you type t.^2 instead of just t^2 ? t is a symbol. same for
the sig symbol.

--Nasser

Subject: laplace function error?

From: G

Date: 20 Sep, 2010 11:29:04

Message: 3 of 3

Okay cool thanks!

Nasser Abbasi <nma@12000.org> wrote in message <0fddbd13-23ce-4510-bf7e-80ec0c99ac2e@y32g2000prc.googlegroups.com>...
> On Sep 19, 9:01 pm, "G " <geffglass...@hotmail.com> wrote:
> > Hi All,
> > I am trying to do the laplace of a simple gaussian pulse. When I do the laplace, however, I do not get an answer. The answer just repeats the same equation in brackets just as below. I know the actual laplace/fourier of the gaussian pulse is the same as in the time domain. So is that what this is trying to tell me? If so, how do I begin using this in the laplace domain?
> >
> > This was the code used and the answer:
> >
> > syms t;
> > syms sig;
> > gau = exp(-0.5*(t.^2)*(1/(sig.^2)));
> > laplace(gau)
> >
> > ans =
> >
> > laplace(1/exp(t^2/(2*sig^2)), t, s)
> >
> > Thanks.
>
>
> well, looks like Matlab just can't do this one.
>
> fyi, here is the answer from Mathematica (I renamed your "sig"
> variable as "y")
>
> In[14]:= gau = Exp[ -1/2 * t^2/y^2 ];
>
> LaplaceTransform[gau, t, s]
>
> Out[15]=
>
> E^((s^2 y^2)/2) Sqrt[Pi/2] y (-1+Sqrt[1/y^2] y+Erfc[(s y)/Sqrt[2]])
>
> ps. why you type t.^2 instead of just t^2 ? t is a symbol. same for
> the sig symbol.
>
> --Nasser

Tags for this Thread

No tags are associated with this thread.

What are tags?

A tag is like a keyword or category label associated with each thread. Tags make it easier for you to find threads of interest.

Anyone can tag a thread. Tags are public and visible to everyone.

Contact us