join_gamma features

Question

Hi,

What would be the correspondent of

@join!(%){expand}{3};

in Cadabra2?

Thanks, Andrei

Answer 1

That's still missing in 2.x, you're the first one to notice, should put it a bit higher on the todo list.

For most practical applications, you can get around it by doing a full join and then using take_match, e.g. doing something like

{a,b,c,d,e,f}::Indices;
\Gamma{#}::GammaMatrix(metric=\delta);
ex:= \Gamma_{a b c} \Gamma_{d e};
join_gamma(_);
take_match(_, $Q?? \Gamma_{a b c}$);

which selects the 3-gamma terms (drop the semicolon ';' on the join_gamma to prevent display of the full join). The Q?? wildcard in the last line is needed to select all other factors.