You may also be interested in PyDy which generates optimized C code from symbolic equations of motion. It uses cse under the hood for some of the optimizations. PyDy directly works with the EoMs that are formed from sympy.physics.mechanics.
Jason moorepants.info +01 530-601-9791 On Tue, Jun 7, 2016 at 9:16 PM, Aaron Meurer <[email protected]> wrote: > Yep. It's called cse(). > > Aaron Meurer > > > On Tuesday, June 7, 2016, Richard Fateman <[email protected]> wrote: > >> 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]> wrote: >>> >>>> On Tue, Jun 7, 2016 at 8:58 AM, Michi S <[email protected]> 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]. >>>> > 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/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]. >>>> 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/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 >> <https://groups.google.com/d/msgid/sympy/d5c4525a-207a-4561-8c8e-8ec397bef4c3%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> 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/CAKgW%3D6%2BAmqPi5kMO6OtBeeeSmXZW_a7H6jC0zyeLCe77d03-Vw%40mail.gmail.com > <https://groups.google.com/d/msgid/sympy/CAKgW%3D6%2BAmqPi5kMO6OtBeeeSmXZW_a7H6jC0zyeLCe77d03-Vw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sympy" group. 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