Nspire cx CAS - Laplace inverse fails 
I'm trying to calculate that easy integral but I get undef.
When I replaced $\infty$ with $1000$, I got the right answer.
($e^{-1000}$ is zero roughly).
Although this calculator knows that $e^{-\infty} = 0$ (as you can see).
What's the problem?
(I know that there is many programs that can get Laplace transformation easily... I'm trying to fix this issue.)
EDIT:

Well, it worked when I replaced $s$ with $5$.
Isn't there any way to make assumptions?
Or storing a number as a variable and getting the answer in terms of it somehow...
EDIT2:

It worked with a little trick :D
I used the number $e$ or $\pi$ to get the answer in terms of them
 A: I can't be 100% sure that this is why your calculator is doing this, but here is a possibility: 
The integral $\displaystyle\int_{0}^{\infty}e^{-st}\,dt$ converges to $\dfrac{1}{s}$ only if $\text{Re}[s]  > 0$. 
However, the integral $\displaystyle\int_{0}^{1000}e^{-st}\,dt$ equals $\dfrac{1}{s} - \dfrac{e^{-1000s}}{s}$ for any value of $s$ except $0$. 
If the calculator made the assumption that $s \neq 0$ but doesn't know to assume $\text{Re}[s]  > 0$, then it might think the first integral isn't defined, while correctly outputting the value for the 2nd integral.
A: It's an old question but the answer might help someone :
In fact you just have to define $s$ as $s>0$ with the '|' symbol, like this (screenshot in the link) :
Usage of the '|' symbol to define assumption for $s$
You can use '|' whenever you have to specify an assumption to the calculator.
A: Try this program, It's for the TI nspire cx cas it does Laplace & inverse Laplace including the Dirac (impulse) and Heaviside step functions. the instructions are in French. You can always use google to translate the info. http://seg-apps.etsmtl.ca/nspire/enseignement/ETS_specfunc.tns
