distribute wedge

Question

\wedge does not seem to be able to distribute a sum, i.e. \wedge(A, B+C) does not give \wedge(A,B) + \wedge(A,C).

Here is an example with cadabra2 version compiled on August 17, 2017.

A::DifferentialForm(degree=1).
B::DifferentialForm(degree=2).
C::DifferentialForm(degree=3).
d{#}::ExteriorDerivative.
ex:=C= d{B}+A ^ B;
ge:=d{C}+A ^ C;
substitute(ge,ex);

produces:

C= dB + A \wedge B
dC + A \wedge C
d (dB + A \wege B) +  A \wedge dB + A \wedge B

Answer 1

The bug is not so much that distribution does not happen automatically (more on that below), but that the last term is manifestly wrong (there should be no A ^ B in the answer). I don't know how that slipped the net, but it's embarrassing... Will fix.

Now the distribution thing. In Cadabra, distribution of operators over sums is not automatic, you need to call

distribute(ge);

explicitly to make that happen. Similarly, the product rule is not applied automatically; you need to call

product_rule(ge);

explicitly. If you do want this to happen automatically, define your post_process function to read something like

def post_process(ex):
   distribute(ex)
   sort_product(ex)
   collect_terms(ex)

(you can stick this in the first cell of the notebook).

Answer 2

This is now fixed in the version on github, thanks for reporting the issue.

(The problem was actually a printing problem, not a maths issue, but I fixed a few other things along the way as well).