K^{EL}_{KnA,KnB} stands here for the respective coefficient at the element “E1” related to the balance at the knot “KnA” (see solution vector) and the derivation over the unkown, which is here the temperature T at the knot “KnB”. Hence, the second, subscripted index of the knot number needs to correspond to the unkown which is here the temperature T_{KnB}.