c234567---------------------------------------------------------------72
c================== calcolo funzioni di forma per l'isoparam. 4 nodi ===
      subroutine defN(xieta, N)
      implicit none

      include 'dim.for'

      double precision xieta(ncrd), N(nnode)

      N(1) = (1d0-xieta(1))*(1d0-xieta(2))/4d0
      N(2) = (1d0+xieta(1))*(1d0-xieta(2))/4d0
      N(3) = (1d0+xieta(1))*(1d0+xieta(2))/4d0
      N(4) = (1d0-xieta(1))*(1d0+xieta(2))/4d0
     
      return
      end subroutine

c234567---------------------------------------------------------------72
c========= calcolo derivate funzioni di forma per l'isoparam. 4 nodi ===
      subroutine defdN(xieta,dN)
      implicit none
      
      include 'dim.for'
      
      double precision xieta(ncrd), dN(ncrd,nnode)
      
      dN(1,1) = -(      1d0 -xieta(2))/4.d+0
      dN(1,2) =  (      1d0 -xieta(2))/4.d+0
      dN(1,3) =  ( xieta(2) +     1d0)/4.d+0
      dN(1,4) = -( xieta(2) +     1d0)/4.d+0
      dN(2,1) = -(      1d0 -xieta(1))/4.d+0
      dN(2,2) = -( xieta(1) +1d0     )/4.d+0
      dN(2,3) =  ( xieta(1) +1d0     )/4.d+0
      dN(2,4) =  (      1d0 -xieta(1))/4.d+0

      return
      end