Ivar KJELBERG
COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted:
1 decade ago
Jan 14, 2011, 6:41 a.m. EST
Hi
First of all this applies only to dependent variables w.r.t. space variables.
So if you have defined a dependent variable "u" of the space x,y,z COMSOl will generate ux, uxx, uy, uyy, uz, uzz, uxy, uxz, uyz, ut, utt (see he doc) all first or second derivative w.r.t. space variable x,y,z respectively or the time "t"
but (pls check I do not know if it i fully true) you need to use the d(,) operator to get a derivative of something else than a depedent variable, and I believe you can only derive w.r.t x,y,z, r,phi or t (to be confirmed). But it's all written in the doc, use an indexer to help you find things in there
--
Good luck
Ivar
Hi
First of all this applies only to dependent variables w.r.t. space variables.
So if you have defined a dependent variable "u" of the space x,y,z COMSOl will generate ux, uxx, uy, uyy, uz, uzz, uxy, uxz, uyz, ut, utt (see he doc) all first or second derivative w.r.t. space variable x,y,z respectively or the time "t"
but (pls check I do not know if it i fully true) you need to use the d(,) operator to get a derivative of something else than a depedent variable, and I believe you can only derive w.r.t x,y,z, r,phi or t (to be confirmed). But it's all written in the doc, use an indexer to help you find things in there
--
Good luck
Ivar
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Jan 14, 2011, 11:23 a.m. EST
Hi
First of all this applies only to dependent variables w.r.t. space variables.
So if you have defined a dependent variable "u" of the space x,y,z COMSOl will generate ux, uxx, uy, uyy, uz, uzz, uxy, uxz, uyz, ut, utt (see he doc) all first or second derivative w.r.t. space variable x,y,z respectively or the time "t"
but (pls check I do not know if it i fully true) you need to use the d(,) operator to get a derivative of something else than a depedent variable, and I believe you can only derive w.r.t x,y,z, r,phi or t (to be confirmed). But it's all written in the doc, use an indexer to help you find things in there
--
Good luck
Ivar
Hi, Ivar, Thanks for your answer.
I find the content in doc about the derivative operator. there is a sentence as " The expressions d(u^2,u) and pd(u^2,u) both equal 2*u ", from this we can see that u is not a independent variable as x, y, z or t. Am I right?
[QUOTE]
Hi
First of all this applies only to dependent variables w.r.t. space variables.
So if you have defined a dependent variable "u" of the space x,y,z COMSOl will generate ux, uxx, uy, uyy, uz, uzz, uxy, uxz, uyz, ut, utt (see he doc) all first or second derivative w.r.t. space variable x,y,z respectively or the time "t"
but (pls check I do not know if it i fully true) you need to use the d(,) operator to get a derivative of something else than a depedent variable, and I believe you can only derive w.r.t x,y,z, r,phi or t (to be confirmed). But it's all written in the doc, use an indexer to help you find things in there
--
Good luck
Ivar
[/QUOTE]
Hi, Ivar, Thanks for your answer.
I find the content in doc about the derivative operator. there is a sentence as " The expressions d(u^2,u) and pd(u^2,u) both equal 2*u ", from this we can see that u is not a independent variable as x, y, z or t. Am I right?
Ivar KJELBERG
COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Jan 14, 2011, 4:28 p.m. EST
Hi
take a look at Magnus (he's from COMSOL ;) reply here
www.comsol.eu/community/forums/general/thread/12911/#p34421
--
Good luck
Ivar
Hi
take a look at Magnus (he's from COMSOL ;) reply here
http://www.comsol.eu/community/forums/general/thread/12911/#p34421
--
Good luck
Ivar