Take a look at the docstring for galois_group.  You need to include a
keyword argument for the variable name of the Galois closure:

K.galois_group(name='b')

On Tue, May 1, 2018 at 11:10 AM, Sanketh Menda <[email protected]>
wrote:

> I was trying to do the example in Adjoining a root of the cubic
> <https://doc.sagemath.org/html/en/thematic_tutorials/explicit_methods_in_number_theory/nf_introduction.html#adjoining-a-root-of-the-cubic>
> in Three Lectures about Explicit Methods in Number Theory Using Sage.
> Specifically, I created a field like this:
>
> sage: K.<b> = QQ[a]
>> sage: K
>> Number Field in a with defining
>> polynomial x^6 + 10*x^3 - 2*x^2 + 25
>> sage: a.minpoly()
>> x^6 + 10*x^3 - 2*x^2 + 25
>> sage: b.minpoly()
>> x^6 + 10*x^3 - 2*x^2 + 25
>>
>
> and then tried to compute the order of the Galois group:
>
>> K.galois_group().order()
>>
>
> This returned a TypeError so I tried to just compute the Galois group:
> K.galois_group(), and even this returns:
>
>>  -----------------------------------------------------------
>> ----------------
>> TypeError                                 Traceback (most recent call
>> last)
>> <ipython-input-41-53b0dca27e76> in <module>()
>> ----> 1 K.galois_group()
>>
>> /Applications/SageMath-8.1.app/Contents/Resources/sage/src/sage/misc/cachefunc.pyx
>> in sage.misc.cachefunc.CachedMethodCaller.__call__
>> (build/cythonized/sage/misc/cachefunc.c:10855)()
>>    2014                 return cache[k]
>>    2015         except KeyError:
>> -> 2016             w = self._instance_call(*args, **kwds)
>>    2017             cache[k] = w
>>    2018             return w
>>
>> /Applications/SageMath-8.1.app/Contents/Resources/sage/src/sage/misc/cachefunc.pyx
>> in sage.misc.cachefunc.CachedMethodCaller._instance_call
>> (build/cythonized/sage/misc/cachefunc.c:10306)()
>>    1890             True
>>    1891         """
>> -> 1892         return self.f(self._instance, *args, **kwds)
>>    1893
>>    1894     cdef fix_args_kwds(self, tuple args, dict kwds):
>>
>> /Applications/SageMath-8.1.app/Contents/Resources/sage/
>> local/lib/python2.7/site-packages/sage/rings/number_field/number_field.pyc
>> in galois_group(self, type, algorithm, names)
>>    5396
>>    5397         if type is None:
>> -> 5398             return GaloisGroup_v2(self, names)
>>    5399
>>    5400         elif type=="pari":
>>
>> /Applications/SageMath-8.1.app/Contents/Resources/sage/
>> local/lib/python2.7/site-packages/sage/rings/number_field/galois_group.pyc
>> in __init__(self, number_field, names)
>>     203
>>     204         if not number_field.is_galois():
>> --> 205             self._galois_closure, self._gc_map =
>> number_field.galois_closure(names=names, map=True)
>>     206         else:
>>     207             self._galois_closure, self._gc_map = (number_field,
>> number_field.hom(number_field.gen(), number_field))
>>
>> /Applications/SageMath-8.1.app/Contents/Resources/sage/
>> local/lib/python2.7/site-packages/sage/rings/number_field/number_field.pyc
>> in galois_closure(self, names, map)
>>    8006               Defn: a |--> 1/240*cc^5 - 41/120*cc
>>    8007         """
>> -> 8008         L, self_into_L = self._galois_closure_and_
>> embedding(names)
>>    8009         if map:
>>    8010             return (L, self_into_L)
>>
>> /Applications/SageMath-8.1.app/Contents/Resources/sage/
>> local/lib/python2.7/site-packages/sage/rings/number_field/number_field.pyc
>> in _galois_closure_and_embedding(self, names)
>>    7923         """
>>    7924         if names is None:
>> -> 7925             raise TypeError("You must specify the name of the
>> generator.")
>>    7926
>>    7927         try:
>>
>> TypeError: You must specify the name of the generator.
>>
>
> On the other hand, K.galois_group(type='gap').order() and
> K.galois_group(type='pari').order() work perfectly.
>
> I am not sure what the error is. It seems to have something to do with the
> new galois_group_v2.
>
> Thanks in advance.
>
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