Comment #7 on issue 3138 by [email protected]: polys expanded representation
problem
http://code.google.com/p/sympy/issues/detail?id=3138
Take simple poly:
p = Poly(x**5)
p
Poly(x**5, x, domain='ZZ')
p.subs(x, y-1)
Poly(x - 1**5, x - 1, domain='ZZ')
p.subs(x, x-1)
Poly(x - 1**5, x - 1, domain='ZZ')
The answer which I expected neither "Poly((x - 1)**5, x - 1, domain='ZZ')"
nor "Poly((x - 1)**5, x, domain='ZZ')"
but this one:
Poly(p.as_expr().subs(x, x-1), p.gens)
Poly(x**5 - 5*x**4 + 10*x**3 - 10*x**2 + 5*x - 1, x, domain='ZZ')
Is not, it?
Can we set the label EasyToFix for it?
The complexity may be for the multivariate polys. Not speak much about the
proper algorithm instead of "as_expr", which can change the generators
incorrectly in common cases.
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