Sign of summation in second order RDTs wrt sextupoles

[blanco-garcia]

Dear all,
I have a doubt about the summation used in the calculation of the second order rdts with respect to sextupoles.

I see that in the elegant file 'twiss.cc' line 4997 the sign of the sum is written as

Code: Select all

termSign = SIGN(ed[iE].s - ed[jE].s);

which is negative for j>i, being j downstream wrt to i.

This termSign is the opposite to the Equation (46) by Chun-Xi Wang "Explicit formulas for 2nd-order driving terms due to sextupoles and chromatic effects of quadrupoles". ANL/APS/LS-330. March 10, 2012.

Is this difference a sign convention in Elegant ? or is there any other reason ?

Best regards,
o