I have a linear map α from Fpn⟶Fpn, where we see Fpn as a vector space over Fp with a Vi as base elements. I want to create the matrix representation for α. For that I have to calculate α(Vi) and then write it in the basis Vi to get my values for the matrix. How exactly do I do the last in sage ? For eg. a polynomial ring it's easy because the elements are already written according to its base but in general thats not the case...