FUNCTION: LieTools/E2R
USAGE: E2R(i);
SYNOPSIS: routines to convert root labeling from -nprts to nprts to a labeling
  from 1 to nrts. When called with a single arguement i, it is necessary to first
  initialize a global Lie algebra environment (see LieTools[gSetup]).
EXAMPLE: 
> LieTools[E2R](1,G2);

                                  7

> LieTools[E2R](-1,G2);

                                  6

> LieTools[E2R](6,G2);

                                  12

SEE ALSO: LieTools[R2E], LieTools[E2G], LieTools[G2E]
