Status: New
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 3402 by [email protected]: replace() should pass objects not
strings to value function
http://code.google.com/p/sympy/issues/detail?id=3402
I'm trying to use replace to apply trigonometric identities:
In [4]: from sympy import Wild, cos, sin
...: from sympy.abc import x,y,p,q
...:
...: expr = p*sin(x)*sin(y) - p*cos(x)*cos(y) + q
...:
...: K = Wild('K', properties=[lambda x: x != 0])
...: A,B,C = map(Wild, 'ABC')
...:
...: def repl(**m):
...: r = K*cos(A+B) + C
...: if ((m['C'] == -m['K']*cos(m['A'])*cos(m['B'])) or
...: (m['C'] == m['K']*sin(m['A'])*sin(m['B']))):
...: return None # this match isn't a real match
...: return r.subs([(Wild(k),v) for k,v in m.items()])
...:
...: expr.replace(K*cos(A)*cos(B) - K*sin(A)*sin(B) + C, repl)
Out[4]: q + K_*cos(x + y)
The Wild K is not substituted because the properties do not match. In this
case, it would be better if repl() was passed a dictionary with Wild
objects rather than strings as keys. This would also be consistent with the
dictionaries returned by match() and subs(map=True), which use objects as
keys.
(if there is an easier alternative way of achieving this simplification I
would of course be happy to hear too!)
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