id,summary,reporter,owner,description,type,status,priority,milestone,component,resolution,keywords,cc,merged,author,reviewer,upstream,work_issues,branch,commit,dependencies,stopgaps
10793,"Matrices can be ""constructed"" from matrices of wrong dimensions",vbraun,jason was,"Let's make a matrix and use it to define a morphism:
{{{
sage: projection = matrix(ZZ,[[1,0,0],[0,1,0]])
sage: projection
[1 0 0]
[0 1 0]
sage: H = Hom(ZZ^3, ZZ^2)
sage: H(projection)
Free module morphism defined by the matrix
[1 0]
[0 0]
[1 0]
Domain: Ambient free module of rank 3 over the principal ideal domain ...
Codomain: Ambient free module of rank 2 over the principal ideal domain ...
}}}
As we see, the matrix of the morphism is very unlikely to be what it should be. Here is the source of the problem:
{{{
sage: projection.parent()
Full MatrixSpace of 2 by 3 dense matrices over Integer Ring
sage: M = MatrixSpace(ZZ, 3 , 2)
sage: M
Full MatrixSpace of 3 by 2 dense matrices over Integer Ring
sage: M(projection)
[1 0]
[0 0]
[1 0]
}}}
So the matrix space converts the input to the matrix no matter what (same with `matrix` command, but inside morphisms matrix spaces are used). I suppose this will work any time the number of entries in the original and in the destination is matching. I think that if one really wants to do it, then this one is very welcome to insert an explicit conversion of a matrix to a list and then back to a matrix, but the above should raise exceptions.
Apply trac_10793_bug_in_matrix_construction.patch, trac_10793_fixing_existing_bugs.patch
",defect,positive_review,critical,sage-4.7.2,linear algebra,,sd31,rbeezer kcrisman,,Andrey Novoseltsev,Volker Braun,N/A,,,,#11200,