Ask Your Question

Revision history [back]

click to hide/show revision 1
initial version

An issue with Root systems in sage

Here is a problem that I cannot seem to understand.


R=RootSystem(['A', 2])
F=R.ambient_space().fundamental_weights()
D=R.ambient_space().simple_roots()
The out-put we get is as follows:

F=Finite family {1: (1, 0, 0), 2: (1, 1, 0)}
D = Finite family {1: (1, -1, 0), 2: (0, 1, -1)}
The issue is the root lattice is contained in the weight lattice but clearly D[2] is not contained in the lattice generated by F. Perhaps I am missing something simple.

I need to write a program I would need the weyl group action on some weights and roots at the same time. How can this be done? Thank you for your time in advance.

An issue with Root systems in sage

Here is a problem that I cannot seem to understand.


R=RootSystem(['A', 2])
F=R.ambient_space().fundamental_weights()
D=R.ambient_space().simple_roots()
The out-put output we get is as follows:

F=Finite family {1: (1, 0, 0), 2: (1, 1, 0)}
D = Finite D=Finite family {1: (1, -1, 0), 2: (0, 1, -1)}
The issue is the root lattice is contained in the weight lattice but clearly D[2] is not contained in the lattice generated by F. Perhaps I am missing something simple.

I need to write a program I would need the weyl group action on some weights and roots at the same time. How can this be done? Thank you for your time in advance.

An issue with Root systems in sage

Here is a problem that I cannot seem to understand.


R=RootSystem(['A', 2])
F=R.ambient_space().fundamental_weights()
D=R.ambient_space().simple_roots()
The output we get is as follows:

F=Finite family {1: (1, 0, 0), 2: (1, 1, 0)}
D=Finite family {1: (1, -1, 0), 2: (0, 1, -1)}
The issue is the root lattice is contained in the weight lattice but clearly D[2] is not contained in the lattice generated by F. Perhaps I am missing something simple.

I need to write a program I would need the weyl group action on some weights and roots at the same time. How can this be done? Thank you for your time in advance.

EDIT: Consider now the Weyl group action on weight lattice. We will continue using the notations above.


W= R.ambient_space(). weyl_group()
S= W.gens()
s1, s2= S
s1.action(F[1]) 
Gives an output
 
ValueError                                Traceback (most recent call last)
<ipython-input-12-4b0b8fd74264> in <module>()
---- 1 s1.action(F[Integer(1)])

/usr/lib/sagemath/local/lib/python2.7/site-packages/sage/combinat/root_system/weyl_group.pyc in action(self, v) 843 """ 844 if v not in self.domain(): --> 845 raise ValueError("{} is not in the domain".format(v)) 846 return self.domain().from_vector(self.__matrixv.to_vector()) 847 ValueError: Lambda[1] is not in the domain

The only way I have been able to make it work is that

L = R. weight_lattice()
F=L.fundamental_weights()
f= L.to_ambient_space-morphism()
s1.action(f(F[1]))
(1,0,0)
This is what I can get but the problem is s2
f(F[2]) = (0,0,1). So we are in a situation of the original problem again. I need to calculate the Weyl group action on the fundamental weights. If there is a better way to do it I would like to know.