I am running equations through the calculus meat grinder that is SymPy, and
I am getting lots of these expressions in my (extremely verbose) results:
sin(a)*cos(b) - sin(b)*cos(a)
of course there is a trigonometric identity that this ought to simplify to,
which is
sin(a-b) = sin(a)*cos(b) - sin(b)*cos(a)
but unfortunately sympy.simplify() does not seem to know about this.
This can be verified like so:
from sympy import *
a,b = symbols('a b')
f = sin(a-b)
f_expanded = expand(f,trig=True)
print f
print f_expanded
f_recovered = simplify(f_expanded)
print f_recovered # no joy
Any ideas on how to automate this simplification? I could go through by
hand but then the whole point is to use SymPy to do this for me (and avoid
pilot error) ...
Thanks for any suggestions,
-Paul
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