Wrong limit?
06-10-2016, 01:48 PM
Post: #1
 whilealive Junior Member Posts: 8 Joined: Sep 2015
Wrong limit?
Hi all.

I got these two different results for a limit (TInspire gets it right). Am I doing something wrong here or is this a bug?

Bests, Bruno
06-10-2016, 02:38 PM
Post: #2
 salvomic Senior Member Posts: 1,366 Joined: Jan 2015
RE: Wrong limit?
If you use lim(expand(...)) it returns ½ also in the Prime

∫aL√0mic (IT9CLU), HP Prime 50g 41CX 71b 42s 12C 15C - DM42 WP34s :: Prime Soft. Lib
06-10-2016, 03:25 PM (This post was last modified: 06-10-2016 03:39 PM by Arno K.)
Post: #3
 Arno K Senior Member Posts: 432 Joined: Mar 2015
RE: Wrong limit?
Well, doing it by hand I get 1/4. Ups, I used a wrong formula, 4*2^n in the middle instead of 4^(2*n).
@Salvo: expand also gives 1/4 on my Prime.
@Bruno: rechecking the screenshots I saw that I used two different formulas
Arno
06-10-2016, 03:32 PM (This post was last modified: 06-10-2016 03:40 PM by salvomic.)
Post: #4
 salvomic Senior Member Posts: 1,366 Joined: Jan 2015
RE: Wrong limit?
(06-10-2016 03:25 PM)Arno K Wrote:  Well, doing it by hand I get 1/4, so TI is wrong and HP is correct.
@Salvo: expand also gives 1/4 on my Prime.
Arno

hi Arno, I used
$\lim_{x\to\infty}( \text{expand} (\frac{2^{4x}+4^{2x}+8^x}{4^{2x+1}}))$
With FW 10077 it should be ½, later I'll control again, however (maybe I'm wrong)...

∫aL√0mic (IT9CLU), HP Prime 50g 41CX 71b 42s 12C 15C - DM42 WP34s :: Prime Soft. Lib
06-10-2016, 03:49 PM
Post: #5
 Arno K Senior Member Posts: 432 Joined: Mar 2015
RE: Wrong limit?
As I inserted above I used the wrong formula, so this is a bug. Imho a very serious one as one usually uses commands like "lim" to keep oneself from these computations.
Arno
06-10-2016, 05:01 PM
Post: #6
 salvomic Senior Member Posts: 1,366 Joined: Jan 2015
RE: Wrong limit?
(06-10-2016 03:49 PM)Arno K Wrote:  As I inserted above I used the wrong formula, so this is a bug. Imho a very serious one as one usually uses commands like "lim" to keep oneself from these computations.
Arno

I agree with you, Arno, a serious bug, apparently so simple but very insidious.
Salvo

∫aL√0mic (IT9CLU), HP Prime 50g 41CX 71b 42s 12C 15C - DM42 WP34s :: Prime Soft. Lib
06-10-2016, 06:40 PM
Post: #7
 whilealive Junior Member Posts: 8 Joined: Sep 2015
RE: Wrong limit?
Thanks for checking. Yes, adding expand() fixes it for me, too. (also FW 10077 here)

Bruno
06-10-2016, 10:17 PM
Post: #8
 roadrunner Member Posts: 292 Joined: Jun 2015
RE: Wrong limit?
Xcas get's it wrong unless you simplify first. Maybe a Giac issue?

06-11-2016, 08:24 AM
Post: #9
 parisse Senior Member Posts: 1,093 Joined: Dec 2013
RE: Wrong limit?
Fix done in source code, I will update the Xcas binaries next week.
It comes from missing simplifications between ln(8), ln(4) and ln(2) not from the limit algorithm itself.
06-11-2016, 09:42 AM
Post: #10
 chromos Member Posts: 184 Joined: Jun 2015
RE: Wrong limit?
(06-11-2016 08:24 AM)parisse Wrote:  Fix done in source code, I will update the Xcas binaries next week.

Although I don't use this advanced mathematics much, I want to say: thank you for very fast bug fixes.

Geocaching Coords Solver, Number of triangles Puzzle
06-12-2016, 08:42 AM
Post: #11
 DrD Senior Member Posts: 1,124 Joined: Feb 2014
RE: Wrong limit?
(06-11-2016 08:24 AM)parisse Wrote:  Fix done in source code, I will update the Xcas binaries next week.
It comes from missing simplifications between ln(8), ln(4) and ln(2) not from the limit algorithm itself.

Do the missing simplifications of ln(x), in the limit() command, effect any other commands, (those that might rely on those same simplification code blocks); or is this just a local problem within the limit command?

Thanks for the quick fixes!

-Dale-
06-16-2016, 07:16 AM
Post: #12
 retoa Member Posts: 168 Joined: Jan 2015
RE: Wrong limit?
A part from the bug, the first image in Bruno's post is quite funny.
I don't know if you noticed that, but the app title is in german (Erweiterte Grafiken) and the error message is in french (Fonctionne seulement en mode radians...)
Menus are in german (Spch for Speichern)

So you have two different languages at the same time. (three if you count the Simplify menu)

How can it be?
06-16-2016, 09:28 AM
Post: #13
 DrD Senior Member Posts: 1,124 Joined: Feb 2014
RE: Wrong limit?
(06-16-2016 07:16 AM)retoa Wrote:  How can it be?

One [possible] very corporate explanation: "honor diversity?"

-Dale-
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