function V = volume(coor)
global coor0, global vec0, global B, global vol0,

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];
V=0;
for i=1:n
 for k=1:N
  x=pint(1,k)*coor(i,:)'+pint(2,k)*coor(i+1,:)';
  V=V+A(k)*2*pi/3*normal(i,1:2)*x*x(1)*jac(i);
 endfor
endfor 
end