Comment #1 on issue 2408 by [email protected]: Error in rsolve
http://code.google.com/p/sympy/issues/detail?id=2408
Sorry, the last 2 lines should read:
The expected answer is f(0)*2**(n-1)*n
f(n) = (2*n/(n-1))*f(n-1) =
(2*n/(n-1))*(2*(n-1)/(n-2))*f(n-2)=...=2**n*FallingFactorial(n,n-1)/(n-1)!f(1)=2**(n-1)*n*f(1)
It seems like the rsolve made the same mistake I did on the post before, to
keep unrolling the recurrence, even though the new term can not be
evaluated.
Even more if one specifies {f(1):1} it generates an error.
In [2]: print rsolve(2*f(-1 + n) + (1 - n)*f(n)/n,f(n),{f(1):1})
ERROR: An unexpected error occurred while tokenizing input
The following traceback may be corrupted or invalid
The error message is: ('EOF in multi-line statement', (2611, 0))
---------------------------------------------------------------------------
CoercionFailed Traceback (most recent call last)
/home/skreft/sympy/sympy/<ipython console> in <module>()
/home/skreft/sympy/sympy/sympy/solvers/recurr.pyc in rsolve(f, y, init)
751 equations.append(eq)
752
--> 753 result = solve(equations, *symbols)
754
755 if result is None:
/home/skreft/sympy/sympy/sympy/solvers/solvers.pyc in solve(f, *symbols,
**flags)
362 for g in f:
363
--> 364 poly = g.as_poly(*symbols)
365
366 if poly is not None:
/home/skreft/sympy/sympy/sympy/core/basic.pyc in as_poly(self, *gens,
**args)
760
761 try:
--> 762 poly = Poly(self, *gens, **args)
763
764 if not poly.is_Poly:
/home/skreft/sympy/sympy/sympy/polys/polytools.pyc in __new__(cls, rep,
*gens, **args)
99 return cls._from_poly(rep, opt)
100 else:
--> 101 return cls._from_expr(rep, opt)
102
103 @classmethod
/home/skreft/sympy/sympy/sympy/polys/polytools.pyc in _from_expr(cls, rep,
opt)
207 """Construct a polynomial from an expression. """
208 rep, opt = _dict_from_expr(rep, opt)
--> 209 return cls._from_dict(rep, opt)
210
211 def __getnewargs__(self):
/home/skreft/sympy/sympy/sympy/polys/polytools.pyc in _from_dict(cls, rep,
opt)
152
153 if domain is None:
--> 154 domain, rep = construct_domain(rep, opt=opt)
155 else:
156 for monom, coeff in rep.iteritems():
/home/skreft/sympy/sympy/sympy/polys/constructor.pyc in
construct_domain(obj, **args)
202
203 coeffs = map(sympify, coeffs)
--> 204 result = _construct_simple(coeffs, opt)
205
206 if result is not None:
/home/skreft/sympy/sympy/sympy/polys/constructor.pyc in
_construct_simple(coeffs, opt)
52
53 for coeff in coeffs:
---> 54 result.append(domain.from_sympy(coeff))
55
56 return domain, result
/home/skreft/sympy/sympy/sympy/polys/domains/pythonrationalfield.pyc in
from_sympy(self, a)
32 return PythonRationalType(*RR.as_integer_ratio(a))
33 else:
---> 34 raise CoercionFailed("expected `Rational` object,
got %s" % a)
35
36 def from_ZZ_python(K1, a, K0):
CoercionFailed: expected `Rational` object, got oo
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