Hello Christophe,
Thanks for your answer.
OK. So if my equation is not solvable symbolically, I can't use SymPy? Then
I will use a numeric solver, like SciPy.
And what does mean
> PolynomialError: 1/log(c2 + 1) contains an element of the generators set
>
when using the function
roots
?
Cheers,
Camille
Le mardi 17 juin 2014 09:45:24 UTC+2, Christophe Bal a écrit :
>
> Hello.
>
> Does your equation solvable symbolically ? At a first glance, I don't
> think.
>
> C.
>
>
> 2014-06-16 10:39 GMT+02:00 Camille Chambon <camille...@gmail.com
> <javascript:>>:
>
>> Hello,
>>
>> I would like to find
>> c2
>> as
>> 0.66 + 0.34 * (1 + 1.0 / c2) - 1.0 / ln(1 + c2) - 0.7 == 0
>> Thus I used the function
>> solve
>> like so:
>> c2 = Symbol('c2')
>> solve(0.66 + 0.34 * (1 + 1.0 / c2) - 1.0 / ln(1 + c2) - 0.7, c2)
>> But I got the following error:
>>
>> NotImplementedError Traceback (most recent call
>>> last)
>>> <ipython-input-86-f1264f7163f3> in <module>()
>>> ----> 1 solve(0.66 + 0.34 * (1 + 1.0 / c2) - 1.0 / ln(1 + c2) - 0.7, c2)
>>>
>>> /usr/lib/python2.7/site-packages/sympy/solvers/solvers.pyc in solve(f,
>>> *symbols, **flags)
>>> 883
>>> ###########################################################################
>>> 884 if bare_f:
>>> --> 885 solution = _solve(f[0], *symbols, **flags)
>>> 886 else:
>>> 887 solution = _solve_system(f, symbols, **flags)
>>>
>>> /usr/lib/python2.7/site-packages/sympy/solvers/solvers.pyc in _solve(f,
>>> *symbols, **flags)
>>> 1382 if result is False:
>>> 1383 raise NotImplementedError(msg +
>>> -> 1384 "\nNo algorithms are implemented to solve equation %s" %
>>> f)
>>> 1385
>>> 1386 if flags.get('simplify', True):
>>>
>>> NotImplementedError: multiple generators [c2, log(c2 + 1)]
>>> No algorithms are implemented to solve equation 3/10 - 1/log(c2 + 1) +
>>> 17/(50*c2)
>>>
>>
>> I read at
>> http://docs.sympy.org/dev/tutorial/solvers.html#solving-equations-algebraically
>>
>> that this error often means that the solution cannot be represented
>> symbolically. Is it the case of my equation?
>> If I can't use solve to find
>> c2
>> , then what can I use?
>> I already tried to use the function
>> roots
>> like so:
>> c2 = Symbol('c2')
>> roots(0.66 + 0.34 * (1 + 1.0 / c2) - 1.0 / ln(1 + c2) - 0.7, c2)
>> Then I got this error:
>>
>>> PolynomialError Traceback (most recent call
>>> last)
>>> <ipython-input-94-fe98ccb57669> in <module>()
>>> ----> 1 roots(0.66 + 0.34 * (1 + 1.0 / c2) - 1.0 / ln(1 + c2) - 0.7, c2)
>>>
>>> /usr/lib/python2.7/site-packages/sympy/polys/polyroots.pyc in roots(f,
>>> *gens, **flags)
>>> 759 else:
>>> 760 try:
>>> --> 761 f = Poly(f, *gens, **flags)
>>> 762 except GeneratorsNeeded:
>>> 763 if multiple:
>>>
>>> /usr/lib/python2.7/site-packages/sympy/polys/polytools.pyc in
>>> __new__(cls, rep, *gens, **args)
>>> 93 return cls._from_poly(rep, opt)
>>> 94 else:
>>> ---> 95 return cls._from_expr(rep, opt)
>>> 96
>>> 97 @classmethod
>>>
>>> /usr/lib/python2.7/site-packages/sympy/polys/polytools.pyc in
>>> _from_expr(cls, rep, opt)
>>> 203 def _from_expr(cls, rep, opt):
>>> 204 """Construct a polynomial from an expression. """
>>> --> 205 rep, opt = _dict_from_expr(rep, opt)
>>> 206 return cls._from_dict(rep, opt)
>>> 207
>>>
>>> /usr/lib/python2.7/site-packages/sympy/polys/polyutils.pyc in
>>> _dict_from_expr(expr, opt)
>>> 325
>>> 326 if opt.gens:
>>> --> 327 rep, gens = _dict_from_expr_if_gens(expr, opt)
>>> 328 else:
>>> 329 rep, gens = _dict_from_expr_no_gens(expr, opt)
>>>
>>> /usr/lib/python2.7/site-packages/sympy/polys/polyutils.pyc in
>>> _dict_from_expr_if_gens(expr, opt)
>>> 266 def _dict_from_expr_if_gens(expr, opt):
>>> 267 """Transform an expression into a multinomial form given
>>> generators. """
>>> --> 268 (poly,), gens = _parallel_dict_from_expr_if_gens((expr,),
>>> opt)
>>> 269 return poly, gens
>>> 270
>>>
>>> /usr/lib/python2.7/site-packages/sympy/polys/polyutils.pyc in
>>> _parallel_dict_from_expr_if_gens(exprs, opt)
>>> 171 coeff.append(factor)
>>> 172 else:
>>> --> 173 raise PolynomialError("%s contains
>>> an element of the generators set" % factor)
>>> 174
>>> 175 monom = tuple(monom)
>>>
>>> PolynomialError: 1/log(c2 + 1) contains an element of the generators set
>>>
>>
>> What does that mean ?
>> Thank you in advance for your help.
>>
>> Cheers,
>>
>> Camille
>>
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