Status: Valid
Owner: ----
Labels: Type-Defect Priority-Medium Polynomial WrongResult
New issue 3245 by [email protected]: Wrong result with Poly.eval
http://code.google.com/p/sympy/issues/detail?id=3245
In [370]: print A
[-alpha*x**2 + x - y]
[ -alpha*y - x*y + x]
In [371]: A.jacobian([x, y]).subs({x:0, y:0}).charpoly().eval((z + 1)/(z -
1))
Out[371]:
2
z + 4⋅z - 1
────────────
2
z - 2⋅z + 1
But the right answer is
In [372]: print A.jacobian([x, y]).subs({x:0, y:0}).charpoly().as_expr()
_lambda**2 + _lambda*(alpha - 1) - alpha + 1
In [373]: f = l**2 + l*(alpha - 1) - alpha + 1
In [374]: f.subs(l, (z + 1)/(z - 1)).cancel()
Out[374]:
2
2⋅α⋅z - 2⋅α + z + 3
────────────────────
2
z - 2⋅z + 1
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