Adding two rings fails unexpectedly

[aheinle@…]

Hello Singular Team,

I have played a bit with different definitions of G-Algebras, and I noticed something that is confusing:

> LIB "./ncfactor.lib"; 
> ring R = (0,q),(x,d),dp;
> def r = nc_algebra(1/q,1);
> setring r;
> basering;
//   characteristic : 0
//   1 parameter    : q
//   minpoly        : 0
//   number of vars : 2
//        block   1 : ordering dp
//                  : names    x d
//        block   2 : ordering C
//   noncommutative relations:
//    dx=1/(q)*xd+1
> ring S = (0,q),(a(1..2),b(1..3)),dp;
> basering;
//   characteristic : 0
//   1 parameter    : q
//   minpoly        : 0
//   number of vars : 5
//        block   1 : ordering dp
//                  : names    a(1) a(2) b(1) b(2) b(3)
//        block   2 : ordering C
> def W = r + S;
// ** Not defined: Cannot map a rational fraction and make a
polynomial out of it! Ignoring the denumerator.
> setring W; basering;
//   characteristic : 0
//   1 parameter    : q
//   minpoly        : 0
//   number of vars : 7
//        block   1 : ordering dp
//                  : names    x d
//        block   2 : ordering dp
//                  : names    a(1) a(2) b(1) b(2) b(3)
//        block   3 : ordering C
//   noncommutative relations:
//    dx=x*d+1

As you see, the non-commutative relation gets messed up when trying to add r to S. I discussed this behaviour with Viktor Levandovskyy, and he confirmed that this is unexpected. Somehow, the objects in the two subrings are not mapped properly.

[hannes]

fixed: requires that the coefficient filed of both summand are equal (see 42127b58bb47458fc008fa5205a12b241d6ca585)