/** partial derivative of to-side reactive power w.r.t to-side voltage angle */
 public float getdTQdTVa() {
   return _list.getdTQdTVa(_ndx);
 }
 /** partial derivative of to-side active power w.r.t. from-side voltage angle */
 public float getdTPdFVa() {
   return _list.getdTPdFVa(_ndx);
 }
 /** partial derivative of to-side reactive power w.r.t. from-side voltage magnitude */
 public float getdTQdFVm() {
   return _list.getdTQdFVm(_ndx);
 }
 /** partial derivative of to-side active power w.r.t. to-side voltage magnitude */
 public float getdTPdTVm() {
   return _list.getdTPdTVm(_ndx);
 }