I think you are merely trying to find common subexpressions to speed up evaluation. There are lots of ways to do that. The simplest is to precompute sin(t), cos(t), exp(t) or whatever non-elementary functions are involved. Then you can also consider using horner's rule or something like factor. But there should be a common-subexpression extraction program around, no? RJF
On Tuesday, June 7, 2016 at 11:39:20 AM UTC-7, brombo wrote: > > You might want to look at "New Foundations for Classical Mechanics" by > David Hestenes and the rigid body rotor description of equations of motion. > > > http://www.amazon.com/Foundations-Classical-Mechanics-Fundamental-Theories/dp/0792353021 > > Should be in your school library. > > > > On Tue, Jun 7, 2016 at 1:14 PM, Aaron Meurer <[email protected] > <javascript:>> wrote: > >> On Tue, Jun 7, 2016 at 8:58 AM, Michi S <[email protected] <javascript:>> >> wrote: >> > >> > Thanks for the answers! For the purpose of my master thesis I am trying >> to >> > optimize the simulaion of helicopter dynamics. These dynamics are pretty >> > complicated, which leads to huge equations for most states. In order to >> > speed up the calculation I need to detect functions that where already >> > evaluated. The inner derivative that is produced due to the chain rule >> is >> > such a function, that I need to detect. >> > >> > factor() works only for the first derivative unfortunately. In the >> second >> > and higher derivatives it does not factorize the inner derivates >> anymore: >> > >> > t = sym.symbols('t') >> > diff( (sin(t)+exp(t))**5 , t ) >> >>> (exp(t) + sin(t))**4*(5*exp(t) + 5*cos(t)) >> > >> > factor(diff( (sin(t)+exp(t))**5 , t )) >> >>> 5*(exp(t) + sin(t))**4*(exp(t) + cos(t)) >> > >> > factor(diff( (sin(t)+exp(t))**5 , t, t )) >> >>> 5*(exp(t) + sin(t))**3*(5*exp(2*t) + 8*exp(t)*cos(t) - sin(t)**2 + >> >>> 4*cos(t)**2) >> >> What output were you expecting here? I don't think the second factor >> can be factorized. Note however that it can be simplified slightly if >> you call trigsimp() on it. >> >> Aaron Meurer >> >> > >> > >> > I think, writing my own differentiation programm will be a little bit to >> > hard to solve my issue. Is there no other way besides factor() and >> wiriting >> > my own programm? >> > >> > >> > Thank for your help! >> > >> > >> > Am Mittwoch, 1. Juni 2016 15:34:28 UTC+2 schrieb Michi S: >> >> >> >> Hello! >> >> >> >> Is there a way to turn off the automatic simplification by calculating >> the >> >> derivative of a function? For example >> >> >> >> t = sym.symbols('t') >> >> sym.Derivative( (sin(t)+exp(t))**3 , t ).doit() >> >> >> >> gives: >> >> (exp(t) + sin(t))**2*(3*exp(t) + 3*cos(t)) >> >> >> >> I need the result without any simplifications (in order to detect the >> >> inner derivative for further calculations) >> >> >> >> Should be: >> >> (exp(t) + sin(t))**2*3*(exp(t) + cos(t)) >> > >> > -- >> > You received this message because you are subscribed to the Google >> Groups >> > "sympy" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> an >> > email to [email protected] <javascript:>. >> > To post to this group, send email to [email protected] >> <javascript:>. >> > Visit this group at https://groups.google.com/group/sympy. >> > To view this discussion on the web visit >> > >> https://groups.google.com/d/msgid/sympy/c5e1f95e-d5e2-4334-b302-39bd6e2ebc9b%40googlegroups.com >> . >> > >> > For more options, visit https://groups.google.com/d/optout. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sympy" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> To post to this group, send email to [email protected] <javascript:> >> . >> Visit this group at https://groups.google.com/group/sympy. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/sympy/CAKgW%3D6J%3D%3Dq4K17wnEvJFagB3URSbJO9CHAjhDJ%3D6a6iQdbZ-gA%40mail.gmail.com >> . >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/d5c4525a-207a-4561-8c8e-8ec397bef4c3%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
