Hello, Buddy

Is it correctly that dphi=[d(phi)/d(x), d(phi)/d(y)]?

dphideta is shape function derivatives in the eta direction. Is eta ont of the axis of local element coordination? If it is so, Which direction is eta? If the local element coordiantion is  (psi, eta, gamma), Why do not define dphidpsi, dphidgamma?

Shenglixu