wrong mixed second derivateves

#1 Posted: 6/25/2012 4:17:37 AM

325 likes in 2052 posts.

Group: Moderator

Hello,

Look at this please
[MATH=eng]f:el(x,1)^3+el(x,2)^3[/MATH]

This is correct:
[MATH=eng]diff(diff(f,el(x,1)),el(x,2))=0[/MATH]

But this is obviously wrong:
v0.95
[MATH=eng]diff(diff(f,el(x,2)),el(x,1))=-el(x,2)*(-1+el(x,2))[/MATH]

It seems that is still present in v.90 as well:
v0.90
[MATH=eng]diff(diff(f,el(x,2)),el(x,1))—-(-1+el(x,2))*el(x,2)[/MATH]

In v0.89.8 you will get the right answer - zeros for both mixed derivatives.

Regards,
Radovan

When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!"

#2 Posted: 7/30/2012 3:14:57 AM

Radovan Omorjan

325 likes in 2052 posts.

Group: Moderator

Hello,

This is still present in 0.95 build 4594 (30 July 2012).

Any comments?

Regards,
Radovan

When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!"

#3 Posted: 7/30/2012 6:59:59 PM

Davide Carpi

1417 likes in 2873 posts.

Group: Moderator

Hi omorr,

Wrote
Hello,

This is still present in 0.95 build 4594 (30 July 2012).

Any comments?

Regards,
Radovan

I confirm!

seem related to the symbolic simplification (see the attachments)

regards,

w3b5urf3r

derivatives_debug.sm (36 KiB) downloaded 70 time(s).

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1 users liked this post

Radovan Omorjan 7/31/2012 1:55:00 AM

#4 Posted: 10/8/2012 7:26:09 PM

Davide Carpi

1417 likes in 2873 posts.

Group: Moderator

Here some (probably) related issues.

best regards,

w3b5urf3r

If you like my plugins please consider to support the program buying a license; for personal contributions to me: paypal.me/dcprojects

#5 Posted: 10/10/2012 4:33:54 PM

Ruben Sidranski

17 likes in 463 posts.

Group: User

It's the way SMath handles/prioritizes ASCII characters. I ran into a similar issue with MathCAD. In this case, the second variable of "x" (in the equation) has to be the first variable of the first derivative as shown in w3b5urf3r's screen shot.

#6 Posted: 5/3/2013 4:11:41 PM

Radovan Omorjan

325 likes in 2052 posts.

Group: Moderator

Hello,

I must be boring with this

, but I think there is neither solution nor satisfactory explanation of this "glitch" regarding second derivatives.
Still present in 0.96

Regards,
Radovan