Issue 1168: Matrix([[x+y, -x, 0], [-x-y, x, 1], [0,1,0]]).inf() gives wrong
result
http://code.google.com/p/sympy/issues/detail?id=1168
New issue report by ondrej.certik:
In [1]: A = Matrix([[x+y, -x, 0], [-x-y, x, 1], [0,1,0]])
In [2]: Ainv = A.inv("ADJ")
In [3]: Ainv
Out[3]:
⎡ -1 -x ⎤
⎢────── 0 ──────⎥
⎢-x - y -x - y⎥
⎢ ⎥
⎢ 0 0 1 ⎥
⎢ ⎥
⎣ 1 1 0 ⎦
In [4]: Ainv*A
Out[4]:
⎡ x y ⎤
⎢- ────── - ────── 0 0⎥
⎢ -x - y -x - y ⎥
⎢ ⎥
⎢ 0 1 0⎥
⎢ ⎥
⎣ 0 0 1⎦
In [6]: (Ainv*A).applyfunc(simplify)
Out[6]:
⎡1 0 0⎤
⎢ ⎥
⎢0 1 0⎥
⎢ ⎥
⎣0 0 1⎦
This is a-ok. But this is wrong:
In [1]: A = Matrix([[x+y, -x, 0], [-x-y, x, 1], [0,1,0]])
In [2]: Ainv = A.inv()
In [3]: Ainv = Ainv.applyfunc(simplify)
In [4]: Ainv
Out[4]:
⎡0 0 0⎤
⎢ ⎥
⎢0 0 1⎥
⎢ ⎥
⎣0 1 0⎦
In [5]: Ainv * A
Out[5]:
⎡ 0 0 0⎤
⎢ ⎥
⎢ 0 1 0⎥
⎢ ⎥
⎣-x - y x 1⎦
It needs to be investigated if the error is in simplify() or in the
inversion algorithm.
See also this thread:
http://groups.google.com/group/sympy/browse_thread/thread/313238d56bbaea21
Issue attributes:
Status: Accepted
Owner: ----
Labels: Type-Defect Priority-High WrongResult
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