INDEX _ _ _ _ _ _ _ _ _ _ _ _ declaration

The declaration index flags a four-vector as an index for subsequent high-energy physics calculations.

syntax:

index<vector-id>{,<vector-id>}*

<vector-id> must have been declared of type vector.

examples:

vector aa,bb,cc; 

index uu; 

let aa.bb = 0; 

(aa.uu)*(bb.uu); 

  0 


(aa.uu)*(cc.uu); 

  AA.CC

Index variables are used to represent contraction over components of vectors when scalar products are taken by the . operator, as well as indicating contraction for the eps operator or metric tensor.

The special status of a vector as an index can be revoked with the declaration remind. The object remains a vector, however.