function E = energy(coor)
global B,
n=max(size(coor))-1;
N=3; xi=[-sqrt(3/5),0,sqrt(3/5)];A=[5/9,8/9,5/9];
pint=[(1-xi)/2;(1+xi)/2];
d=[coor(2:n+1,:)-coor(1:n,:)];ll=norm(d,"rows");jac=ll/2;
normal=-[d(:,2)./ll,-d(:,1)./ll];
E=0;
for i=1:n
 for k=1:N
  x=pint(1,k)*coor(i,:)'+pint(2,k)*coor(i+1,:)';
  E=E+A(k)*(B*x(2)^2*x(1)*normal(i,2)+2*x(1))*jac(i);
 endfor
endfor 
end