It isn't too pressing for PyDy, I just ran into it when creating some tests that would ensure PyDy gave the same output as Autolev. In Autolev, if you express a UnitVector from one reference in the coordinates of another reference frame that is 3 or more simple rotations away, when you convert the expression back to the original frame, you won't just get a UnitVector. This isn't a huge deal and I don't see immediately a situation where you would go back and forth between frames just for fun, but it would be nice to know that you could if you wanted to :)
I'll file the bug report, and I'll try to look at the paper Akshay mentioned. Akshay, if you need more examples that should simplify, I can provide you with a handful more :) ~Luke On Apr 28, 8:28 am, Akshay Srinivasan <akshaysriniva...@gmail.com> wrote: > I think trigsimp is too hack-ish. I'll try implementing the algorithm > given athttp://vv.cn/d/d.aspx?Id=21987_1.0.42119- I guess this is > the one Ondrej was talking about - in the coming weeks. I'm still not > sure how good it is, does anyone know of anything better ? > > Akshay > > On Apr 28, 6:52 pm, Alan Bromborsky <abro...@verizon.net> wrote: > > > Ondrej Certik wrote: > > > On Tue, Apr 28, 2009 at 12:22 AM, Luke <hazelnu...@gmail.com> wrote: > > > >> I'm writing some tests for some code that expresses a Vector expression > > >> in > > >> the coordinates of a different frame. I am using Sympy's trigsimp to > > >> simplify expressions, but the following Sympy expression isn't > > >> trigsimplifying: > > >> cos(q4)**2 + sin(q3)**2*sin(q4)**2 + cos(q3)**2*cos(q4)**2*tan(q4)**2 > > > >> It should simplify to 1, instead it trigsimplifies to: > > >> cos(q4)**2 + sin(q3)**2*sin(q4)**2 + cos(q3)**2*sin(q4)**2 > > > > It's a bug. Could you please file an issue for it? > > > > There is a nice article how to implement robust trigsimp somewhere in > > > our issues, but noone found time for it yet. > > > > Is it very pressing for pydy? If not, let's keep this in mind and > > > continue --- I think at the end of the summer it will be clear what > > > sympy bugs should be fixed first and which later, so that pydy works > > > reasonably well. > > > > Ondrej > > > Program: > > > from sympy import * > > q3,q4 = symbols('q3,q4') > > f = cos(q4)**2 + sin(q3)**2*sin(q4)**2 + cos(q3)**2*cos(q4)**2*tan(q4)**2 > > print f > > f = trigsimp(f,deep=True,recursive=True) > > f = trigsimp(f,deep=True,recursive=True) > > print f > > > Output: > > > cos(q4)**2 + sin(q3)**2*sin(q4)**2 + cos(q3)**2*cos(q4)**2*tan(q4)**2 > > 1 > > > Note on strange behavior. When I ran this program from SPE I did not > > need the second > > "f = trigsimp(f,deep=True,recursive=True)" to simplify to 1, but when I > > ran it from a shell > > I did. Shell results without second "f = > > trigsimp(f,deep=True,recursive=True)" : > > > cos(q4)**2 + sin(q3)**2*sin(q4)**2 + cos(q3)**2*cos(q4)**2*tan(q4)**2 > > cos(q4)**2 + cos(q3)**2*sin(q4)**2 + sin(q3)**2*sin(q4)**2 > > > Perhaps what trigsimp needs to do is convert all expressions to sin and > > cos and do algebraic simplification > > and then do trigsimp! > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sympy?hl=en -~----------~----~----~----~------~----~------~--~---
