Hello,
I am trying to re-implement most of the code from "Structure and
Interpretation of Classical Mechanics" (Sussman and Wisdom,
http://mitpress.mit.edu/sicm) in sympy. The original language is
their particular dialect of Scheme. I have had success with most of
the first chapter, but with quite a few "kludges": I will mail the
mailing list with details when the code is a bit cleaner.
Currently, I find the following issue:
theta = Function("theta")
phi = Function("phi")
psi = Function("psi")
t = symbols("t")
trigsimp(expand(diff(theta(t),
t)*sin(phi(t))*sin(psi(t))*sin(theta(t)),True,True),True,True)
(output)==> 0
trigsimp(expand(diff(theta(t),
t)*sin(phi(t))*sin(psi(t))*sin(theta(t)),True,True),True,False)
(output)==> D(theta(t), t)*sin(phi(t))*sin(psi(t))*sin(theta(t))
The second answer is correct, the first is wrong. Is there a problem
with recursive evaluation when derivatives are present? I ran into
this problem when trying to simplify the derivative of a matrix.
Without "recursive", non-derivative expressions are rather
inadequately simplified; with "recursive", expressions containing
derivatives apparently return zero.
A previous issue, while I am on the subject: "from sympy import *"
clobbers the Python builtin "sum" function, so eg
sum([1,2,3])
doesn't work. Is that intended?
All this is on Sympy 0.6.6. (Ubuntu 10.04 package). Should I upgrade?
Thanks,
Rahul
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