integrating with the HP Prime
11-12-2016, 08:35 AM (This post was last modified: 11-12-2016 08:38 AM by Fanboy.)
Post: #1
 Fanboy Junior Member Posts: 13 Joined: Mar 2014
integrating with the HP Prime
I'm trying to integrate 'e^(-B*x^2) from -inf to +inf' with the hp prime emulator. The calculator is not spitting out what I'm looking for which is sqrt(pi/B) and incorrectly gives infinity as the answer.

However, it gives the correct answer (sqrt(pi)) when I just integrate 'e^(-x^2) from -inf to +inf' (without any letters). If I use a number instead of a letter, then it starts giving out the correct answer again. I'm completely new to the prime (currently have a 50G) so can anyone tell me how to get my answer in terms of the letter?

I've posted a pic of the problem here:
http://i1226.photobucket.com/albums/ee40...rhavgy.png
11-12-2016, 10:28 AM
Post: #2
 parisse Senior Member Posts: 1,310 Joined: Dec 2013
RE: integrating with the HP Prime
You should not use B as parameter, because B is always assigned on the Prime, by default to 0.0, and since exp(-B*x^2)=1 if B=0 this explains why the integral is infinity. Try with b instead.
11-12-2016, 11:15 PM (This post was last modified: 11-12-2016 11:16 PM by Fanboy.)
Post: #3
 Fanboy Junior Member Posts: 13 Joined: Mar 2014
RE: integrating with the HP Prime
How do we know which letters have a value attached to them like B? I noticed that the letters 'K' and 'A' also gave infinity as the answer.
Also, if I use another letter like b or a, I get the answer as "undef". Its still not working.
11-13-2016, 12:01 AM
Post: #4
 roadrunner Senior Member Posts: 441 Joined: Jun 2015
RE: integrating with the HP Prime
You have to tell it that b isn't negative.

Try typing: assume(b≥0)

Then type: ∫(e^((-b)*x^2),x,-(∞),∞)

You should get: √(π)/√(b)

11-13-2016, 12:21 AM
Post: #5
 Fanboy Junior Member Posts: 13 Joined: Mar 2014
RE: integrating with the HP Prime
Ok, that works. How do I remove that assumption?
11-13-2016, 12:44 AM
Post: #6
 roadrunner Senior Member Posts: 441 Joined: Jun 2015
RE: integrating with the HP Prime
(11-13-2016 12:21 AM)Fanboy Wrote:  How do I remove that assumption?

purge(b)
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