Status: Accepted
Owner: asmeurer
CC: smi...@gmail.com, nicolas....@gmail.com
Labels: Type-Defect Priority-Medium WrongResult Solvers
New issue 2678 by asmeurer: solve does not correctly handle derivatives
http://code.google.com/p/sympy/issues/detail?id=2678
I checked the git history, and I don't think this ever worked:
In [1]: var('x1 x2 t')
Out[1]: (x₁, x₂, t)
In [2]: b = Eq(x2(t).diff(t), x1(t) - 3*x2(t))
In [3]: solve(b, x2(t))
Out[3]:
⎡ ⎛ d ⎞⎤
⎢-⎜-x₁(t) + ──(0)⎟⎥
⎢ ⎝ dt ⎠⎥
⎢─────────────────⎥
⎢ d ⎥
⎢ ──(1) + 3 ⎥
⎣ dt ⎦
The correct answer should be (x1 - x2(t).diff(t))/3. solve() should treat
derivatives of functions as completely independent of the function that
it's solving for.
I think this might have something to do with the part that preprocesses
functions into Dummys so that they are Symbols.
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