Jacobian matrix

Forum|Forum|4 years ago
March 10, 2022
2 replies
7959 views

Hi community

in this simple example,is shown how Mathcad help me to find a singularity value (det J = 0)

Capture d’écran 2022-03-10 114651.jpg

thanks

Mechanical_Engineering

W

Werner_E

25-Diamond I

Is there any question you have???

Why do add and not subtract. Furthermore it looks like you ran into Prime infamous auto-label trap and will have to manually label all variables the same.

Is there any reason you are not using the built-in "Jacob" function?

Would be straightforeward - here done in MC15

W

Werner_E

25-Diamond I

I converted the MC16 to Prime6 and I had to realize that once again Jacobi is one of those things that are broken in Prime. This time its the new symbolic engine which fails. In Prime 6 we still have the option to use the old symbolic engine (muPad) so we can compare:

Legacy Symbolic Engine:

New Symbolic Engine (Axiom fork)

Crap! Didn't wait for the last region to finish calculating.

Don't have P7 installed so I can't say if the bug is already fixed there.

1_Jacob-Test.zip

X

XDN

Author

14-Alexandrite

Of course the solution is exactly your 1st screenshot !

But it's amazing that it doesn't work 😡

should we continue to do this by hand, it's not very serious

W

Werner_E

25-Diamond I

OK, I further looked at the problems with Prime and I still consider it a bug in the new symbolics but there is an easy workaround.

The reason for the bug seems to be that the new symbolic engine is not always able to determine correctly the number of arguments in use. So the workaround is to just use the optional third argument of the "Jacob" function and tell Prime the number of independent variables in use.

There is a further problem in Prime when we try to solve for theta2. Primes new symbolic seems to not like vector indexed variables to solve for. Substituting the vector element for a "normal" variable seems to cure this problem.