On May 5, 10:21 am, Volker Braun <vbraun.n...@gmail.com> wrote:
> Thats a bug. Its tricky because it involves homs from a FreeModule to a
> FGP_Module. If you stay within FGP_Modules then it works:
Great! That has almost everything on it that I need. Intersection and
sum of submodules don't seem to exist yet, though. Should we implement
those somewhere? I think the following two functions do the trick.
Suggestions on improvements and/or naming and/or where they should go?
I would guess they should be methods on
sage.modules.fg_pid.fgp_module.FGP_Module_class
def intersect_submodules(M,S1,S2):
Q1=M/S1
Q2=M/S2
R12=Q1.relations().direct_sum(Q2.relations())
R12ambient=R12.ambient_module()
Q12=R12ambient/R12
return M.hom([Q12(R12ambient(list(Q1(b).lift())
+list(Q2(b).lift()))) for b in M.gens()]).kernel()
def sum_submodules(M,S1,S2):
return M.submodule([M(b) for b in S1.gens()+S2.gens()])
Z3=ZZ^3
M=Z3/Z3.span([36*Z3.0])
S1=M.submodule([6*M.0,3*M.1+3*M.2,3*M.1-3*M.2])
S2=M.submodule([8*M.0,6*M.2])
intersect_submodules(M,S1,S2)
sum_submodules(M,S1,S2)
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