function S=stress_tensor(E,V,volume)
%E - list of edges in entire cellular structure
%V - x-y coordinates of vertices in entire cellular structure
%
%For bugs, comments, clarifications or modifications, please contact Kapil Krishan :
%kkrishan@uci.edu
%www.physics.uci.edu/~foams
%version: I

l_vec=V(E(:,1),:)-V(E(:,2),:);

S=(l_vec'*(l_vec./(sqrt(sum(l_vec.^2,2))*[1 1])))/volume;