function flag=outflow(md); A=md.segments(:,1); B=md.segments(:,2); Nx=-(md.y(A)-md.y(B)); Ny= md.x(A)-md.x(B); Vx=(md.vx(A)+md.vy(B))/2; Vy=(md.vy(A)+md.vy(B))/2; %dot product VdotN=Vx.*Nx+Vy.*Ny; flag=zeros(md.numberofgrids,1); flag(A(find(VdotN>0)))=1;