Nspire cx CAS - Laplace inverse fails

Question

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

Answer 1

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.

Answer 2

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.

Answer 3

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