2018-04-10 17:30:55 -0500 received badge ● Popular Question (source) 2011-02-21 17:59:23 -0500 received badge ● Nice Question (source) 2011-02-13 16:03:22 -0500 received badge ● Scholar (source) 2011-02-13 16:03:22 -0500 marked best answer Dictating the roots to RootSystem Currently, there isn't an easy way to specify the choice of simple roots. If you really want to work with a different set of roots, here's the best way to do it. For the sake of this example, we'll pretend we're working in type A. 1) Create a class MyAmbientSpace which subclasses sage.combinat.root_system.ambient_space.AmbientSpace. The main method you'll need to implement is simple_root(i) which returns the simple root associated with i in the index set. You'll also need implement methods like smallest_base_ring and dimension. See sage.combinat.root_system.type_A for an example. from sage.combinat.root_system.ambient_space import AmbientSpace class MyAmbientSpace(AmbientSpace): def simple_root(self, i): ... ...  2) Create a class MyCartanType which is a subclass of the current Cartan type, and set its AmbientSpace attribute to your MyAmbientSpace class: from sage.combinat.root_system.type_A import CartanType as CartanTypeA class MyCartanType(CartanTypeA): AmbientSpace = MyAmbientSpace  3) Instantiate a root system based on your "new" CartanType: my_a = MyCartanType(3) R = RootSystem(my_a)  That root system should now use the simple roots you specified. 2011-02-13 11:32:19 -0500 asked a question Dictating the roots to RootSystem Is there a way to dictate the choice of roots/simple roots to the RootSystem command? 2010-11-21 19:23:07 -0500 received badge ● Student (source) 2010-11-14 07:25:48 -0500 asked a question Can't make subposets I'm running into a problem trying to construct a subposet. sage: L #poset of permutations Finite poset containing 14 elements sage: L.random_subposet(.5) Finite poset containing 10 elements sage: SPG=ShortestPathGraph(L) #constructs a graph that is the Hasse diagram #of L with some edges deleted sage: SPG Digraph on 14 vertices sage: S=Poset(SPG) sage: S.random_subposet(.5)  results in an error message ending AttributeError: 'Permutation_class' object has no attribute 'parent'  I get the same error when I try to construct a specific subposet (what I actually want to do), but I can't create duplicate the error in a small example. random_subposet() works just fine for a small poset created from a digraph whose vertices are permutations. Any ideas what could be going on? (I suspect whatever it is may have to be in ShortestPathGraph, given that I can't duplicate the error with a small digraph, but that doesn't really make sense, so I'd appreciate that sort of answer as well.)