How do the op counts get into the tens or hundreds of thousands? When the expressions are that complicated I would have thought that it was faster and more numerically accurate to perform whatever symbolic operations are used to obtain those expressions using numerical routines. For example if a matrix is inverted symbolically it would be better to substitute your values and invert the matrix numerically etc. A 3D rotation can be computed very cheaply in floating point with quaternions.
-- Oscar On Tue, 29 Jun 2021 at 12:00, Peter Stahlecker <peter.stahlec...@gmail.com> wrote: > > Dear Jason, > > Thanks! > I tested it right away, and I counted the operations of an entry of rhs = > KM.rhs() > > For ‚Body‘ I got the count 245,633 > With the auxiliary frames the count was 13,235 > > Thanks again and stay healthy! > > I will keep on testing this. > > Peter > > > > > On Tue 29. Jun 2021 at 12:32 Jason Moore <moorepa...@gmail.com> wrote: >> >> Peter, >> >> THey are equivalent other than one may provide a simpler set of direction >> cosine matrices and angular velocity definitions. The "Body" method should >> give simpler equations of motion in the end because we try to use >> pre-simplified forms of the equations. I don't know why you'd see faster >> with the intermediate frame method. >> >> You can use sympy's count_ops() function to see how many operations each >> symbolic form gives. The one with more operations should ultimately be >> slower when lambdified(). >> >> Jason >> moorepants.info >> +01 530-601-9791 >> >> >> On Tue, Jun 29, 2021 at 5:09 AM Peter Stahlecker >> <peter.stahlec...@gmail.com> wrote: >>> >>> When I want to do this, it seems to me there are these possibilities: >>> >>> 1. >>> A = N.orientnew(‚A‘, ‚Body‘, [q1, q2, q3], ‚123‘) >>> This does it in one step >>> >>> 2. >>> I use two intermediate frames and use the word ‚Axis‘ instead of ‚Body‘ >>> >>> Geometrically, this should be the same, but it seems to me, that with the >>> intermediate frames establishing Kane‘s equations, lambdifying them and >>> doing the numerical integration is MUCH faster. >>> >>> Are methods 1 and 2 not equivalent, as I assumed, or am I doing something >>> wrong? >>> >>> Thanks for any explanation! >>> >>> -- >>> 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 sympy+unsubscr...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/sympy/d1597154-f8a8-42fa-b29b-6e8f57062441n%40googlegroups.com. >> >> -- >> 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 sympy+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/sympy/CAP7f1AhvTHkfn8_Wc7L9i7em3QvDHn6MPBHoWwqvK9qOUw3QfA%40mail.gmail.com. > > -- > Best regards, > > Peter Stahlecker > > -- > 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 sympy+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CABKqA0bdrLLiCY7w3yG_3sPTmx7O4Z00tn-mLSssj0rvT4m9QA%40mail.gmail.com. -- 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 sympy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAHVvXxSchAaF6rRig0zL9VF4w3MLyiVra2dZ4vp9vuYDdKyY0w%40mail.gmail.com.
