vermaseren
commented
6 years ago You can handle this in the declaration of the indices. In your case Symbol D,N; Index mu=D,nu=D,a=N,b=N; should do the trick. It causes d(mu,mu) to be replaced by D and d(a,a) by N. Hence your d(mu,nu)*d(mu,nu) will become D as well. Etc.
I hope this is what you are after.
Jos
On 2 Jan 2018, at 22:31, Daniel Fetchinson notifications@github.com wrote:
I'd like to use FORM for summing over and manipulating spacetime indices as well as summing over and manipulating color indices (more generally going from 1 to N). Is it possible? For instance if I have a propagator like $G(\mu,\nu,a,b) = \delta{\mu\nu} / k^2 \delta{a, b}$ then I'd like to be able to do the double trace $G(\mu,\nu,a,b) G(\mu,\nu,a,b) = DN/k^4$ (obviously in actual examples the expressions would be more complicated). How do I specify that one type of index has range 0...(D-1) and the other 1...N? (The latter can also be 0...(N-1) of course, that's no problem.)
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fetchinson
I'd like to use FORM for summing over and manipulating spacetime indices as well as summing over and manipulating color indices (more generally going from 1 to N). Is it possible? For instance if I have a propagator like $G(\mu,\nu,a,b) = \delta{\mu\nu} / k^2 \delta{a, b}$ then I'd like to be able to do the double trace $G(\mu,\nu,a,b) G(\mu,\nu,a,b) = DN/k^4$ (obviously in actual examples the expressions would be more complicated). How do I specify that one type of index has range 0...(D-1) and the other 1...N? (The latter can also be 0...(N-1) of course, that's no problem.)