HOME and CAS unexpected behavior
10-21-2022, 08:35 PM
Post: #1
 mmadurga Junior Member Posts: 1 Joined: Dec 2021
HOME and CAS unexpected behavior
Hi all,

One of my students mentioned to me that he was getting zero when calculating the result of a finite integral in HOME.

I already had the solutionI calculated using a table of integrals so I could easily evaluate it in both HOME and CAS, and, lo and behold, I get 0.000E0 in HOME, 7.1054E-15 in CAS.

The expression to evaluate is

EXP(-2r/a) * (-2r^2/a^2 - 2r/a - 1) + 1

with r=0.877E-15 and a =5.290E-11

Any idea where is this behavior coming from?[/code]
10-22-2022, 06:04 PM (This post was last modified: 10-22-2022 06:12 PM by rawi.)
Post: #2
 rawi Member Posts: 178 Joined: Nov 2019
RE: HOME and CAS unexpected behavior
What are the lower and upper limit of the integral? And what is the variable to integrate?
10-22-2022, 07:13 PM
Post: #3
 Albert Chan Senior Member Posts: 2,711 Joined: Jul 2018
RE: HOME and CAS unexpected behavior
(10-21-2022 08:35 PM)mmadurga Wrote:  I already had the solutionI calculated using a table of integrals so I could easily evaluate it in both HOME and CAS, and, lo and behold, I get 0.000E0 in HOME, 7.1054E-15 in CAS.

Since you use table of integrals, I assumed it has nothing to do with integration routine.

It may be due to massive cancellations, for F(hi) - F(lo)
HOME has 12 decimals precisions, but CAS has more (53-5 = 48-bits, or about 14+ decimals)
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