ufl team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/4/7, Pearu Peterson <pearu@xxxxxxxxx>:
> Martin Sandve Alnæs wrote:
>
>  > I don't agree with the x.T stuff. There is no differentiation between
>  > columns and rows in tensor algebra, so the transpose has no meaning
>  > for a rank 1 tensor. This has to generalize to where x is a rank 1
>  > expression and not only an explicitly constructed vector. If you have
>  > a rank 4 tensor and pick a sub-tensor of rank 1 from it, is it a
>  > column or row? Columns and rows doesn't generalize, and special cases
>  > are evil.
>
>
> Transpose is well-defined also for arbitrary rank tensors. It swaps
>  the first two indices:
>
>    transpose(t_ijkl..) -> t_jikl..
>
>  One can also defined generalised transpose:
>
>    transpose(t_ijkl.., [p_i, p_j, p_k, p_l, ..]) -> t_(p_i)(p_j)(p_k)(p_l)..

We _could_ support something like that, but I don't think it's worth
the trouble since the more general index notation covers this without
making detailed definitions:

# reference components
Aijkl = A[i,j,k,l]
# make tensor with different axis ordering
B = Tensor(Aijkl, (j,i,k,l))

--
Martin