CollectNonScalars collects terms in sums with same tensorial parts. In contrast to standard Redberry behaviour when factored out tersorial parts with nonzero sized idices, CollectNonScalars tries to factor out parts with nonzero sized free indices.Collect same tensorial parts:
//by default, B_m will not be factored out def t = 'A_i*A^i*B_m + B_m'.t println t
> A_i*A^i*B_m + B_m
//now will println CollectNonScalars >> t
> (A_i*A^i + 1)*B_m
Another example:
setSymmetric 'R_mn' println CollectNonScalars >> 'A_t*A^t*R_mn - B_t*B^t*R_nm'.t
> (A_{t}*A^{t}-B_{t}*B^{t})*R_{mn}