Updates:
Labels: -NeedsReview NeedsBetterPatch EasyToFix
Comment #4 on issue 1644 by asmeurer: Coeff() with derivatives and functions
http://code.google.com/p/sympy/issues/detail?id=1644
Yes, that is my code in ode.py. It is caused by the code around line 2025,
which is an algorithm to match a
linear ODE (a_n(x)y^(n) + ... + a_1(x)y' + a_0(x)y + B(x) = 0). It takes
advantage of this bug by getting the
coeff of f(x) on each term, which works if the term is f(x) or if it is a
derivative of f(x), and then it later checks
what the order of the derivative is to collect them in a dictionary.
This behavior is clearly wrong. I was just taking advantage of the way
that it worked at the time. The
algorithm needs to be rewritten to check each derivative successively. It
won't be too difficult. The order and
the function are passed through the arguments of the function. I will do
it when I am free again if no one
else want to do it for me.
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