Problem with Laplace transform

01182016, 11:58 AM
Post: #1




Problem with Laplace transform
Hi !
When i want to do a Laplace transform like : Laplace(u(t),t,p) i want to have for the result : 1/p but didn't have this ... And when i do ILaplace(1/p) i have for result : Dirac/p ... What is the problem ? Ans how can i fix it ? Thanks and have a Nice day ! 

01182016, 02:13 PM
Post: #2




RE: Problem with Laplace transform
Hi
Both the "laplace" and "ilaplace" functions have three parameters: expression, variable of the expression, and variable of the result. The last two variables are optional, but it looks like if you don't specify them, the calculator uses the variable x as the default variable. With firmware 2015 6 17 (8151), you have the following results: laplace(1): 1/x laplace(1,t,p): 1/p ilaplace(1/x): 1 ilaplace(1/p): Dirac(x)/p > wrong ilaplace(1/p,p,t): 1 So, it seems that sometimes the two last variables are necessary, in order to get correct answers. I hope this heps. 

01182016, 03:09 PM
Post: #3




RE: Problem with Laplace transform
The default variable is x, therefore nothing is wrong.


01182016, 04:52 PM
Post: #4




RE: Problem with Laplace transform
You're right.
The case ilaplace(1/p) = Dirac(x)/p is correct because p is interpreted by the HP Prime as a constant. 

01182016, 10:51 PM
(This post was last modified: 01182016 10:52 PM by Natoe.)
Post: #5




RE: Problem with Laplace transform
Thanks ! , but for the U(t) like in this exemple :
http://image.noelshack.com/fichiers/2016...titre.png U(t) on Hp prime = "1" because U(t) = 1/P and when i did : "ilaplace(1/p,p,t)" the result is "1" So i did on the hp prime :"Laplace((1+(t2)².1(t2),t,p) for the exercice and the result is wrong or not the same ... And thanks for your answer ! 

01192016, 08:21 AM
Post: #6




RE: Problem with Laplace transform
I guess that by U(t) you mean the step function. In that case you need to use the HP Prime function Heaviside().
The step function at t=0 is Heaviside(t), and the step function at other values, say t=2, is Heaviside(t2). Using this function you get: laplace(Heaviside(t),t,p) = 1/p laplace(Heaviside(t2),t,p) = e^(2*p)/p laplace(Heaviside(t)+(t2)^2*Heavisede(t2),t,p) = (p^2+2*e^(2*p)) / p^3 

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