Update exputil/EmpCylSL.cc

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: The9Cat

exputil/EmpCylSL.cc

@@ -4109,7 +4109,7 @@ void EmpCylSL::accumulate(double r, double z, double phi, double mass,
       Eigen::VectorXd vC = vc[id].row(mm).transpose() * norm;
       Eigen::VectorXd vS = vs[id].row(mm).transpose() * norm;
 
-      // Make sure we only have real part here
+      // For m = 0, the azimuthal dependence vanishes; set vS to zero to ensure a purely real result
       if (mm==0) vS.setZero();
 
       vec.real() = vC*mcos + vS*msin;