sumCollect

◼ sumCollect[expr] collects sums over the addends.

◼ sumCollect tries to rewrite an expression featuring symbolic sums with sums over common indexes.

◼ See also: sum, sumThread, sumExpand, sumFullSimplify, sumSimplifyKD, sumAbstractIndex, sumNameIndex.

Further examples

Load sneg and declare some quantities.

<< sneg`sneg`;
snegfermionoperators[c]
snegfreeindexes[k, k1, σ]

Collect terms

sum[number[c[k], σ], {k, σ}] - 
      sum[1, {k}]
sumCollect[%]

antikomutator[c[CR, k], 
      sum[c[AN, k1], {k1}]]
sumCollect[%]