Group Abstract Group Abstract

Message Boards Message Boards

0
|
8.2K Views
|
10 Replies
|
4 Total Likes
View groups...
Share
Share this post:

Laplace Transform not working

Russell Barry, Physicist
Posted 11 years ago

I am working on a green's function program to solve PDE's with the DiracDelta function in it. I am using it for some student's and it work's for ODE's but not PDE"S. Can someone tell me why the following is happening. The function g''[x] is obviously a function of x and not t. If you were doing it by hand you can forget integration by parts. When I enter this LaplaceTransform[g''[x], t, s] I get this g''[x]/s Obviously the s should not be on the bottom. Why am I getting this. Same for the first derivative. Enter LaplaceTransform[g'[x], t, s] I get this g'[x]/s still has the s on the bottom. It works if g is a function of t LaplaceTransform[g'[t], t, s] is, -g[0] + s LaplaceTransform[g[t], t, s] which is correct, but now we have g[t] and not g[x]. Since I am writing a program I need the Laplace transform to know the difference.
POSTED BY: Russell Barry
10 Replies
Sort By:
POSTED BY: Sean Clarke
David Keith
David Keith
Posted 11 years ago

However, if I read your post correctly, I think LaplaceTransform is working correctly, in that the Laplace transform of 1 is 1/s.

In[1]:= LaplaceTransform[g'[t], t, s]

Out[1]= -g[0] + s LaplaceTransform[g[t], t, s]

In[2]:= LaplaceTransform[g'[x], t, s]

Out[2]= Derivative[1][g][x]/s

In[3]:= LaplaceTransform[1, t, s]

Out[3]= 1/s
POSTED BY: David Keith
POSTED BY: Russell Barry
POSTED BY: Russell Barry
David Keith
David Keith
Posted 11 years ago

Hi Russel, A nice write-up on posting can be found here How to post including how to put Mathematica code in your post.

Kind regards, David
POSTED BY: David Keith
POSTED BY: Russell Barry

Thank's anyway, I really appreciate you trying to help.

POSTED BY: Russell Barry
POSTED BY: Russell Barry

I think t is just a dummy variable here for integral. It does not matter whether it is x or t. 

LaplaceTransform[g'[t], t, s]

and 

LaplaceTransform[g'[x], x, s]

give me the same result.
POSTED BY: Shenghui Yang
POSTED BY: Russell Barry
Reply to this discussion
Community posts can be styled and formatted using the Markdown syntax.
Tag limit exceeded
Note: Only the first five people you tag will receive an email notification; the other tagged names will appear as links to their profiles.
Reply Preview
Attachments
Remove
or Discard