function idum = plota(xx)
global nb nv barras restric massa
%% plota estado atual
for i=1:nb
	xyloc(1,1) = xx(2*barras(i,1)-1);
	xyloc(1,2) = xx(2*barras(i,1));
	xyloc(2,1) = xx(2*barras(i,2)-1);
	xyloc(2,2) = xx(2*barras(i,2));
        plot(xyloc(:,1),xyloc(:,2));
        hold on;
end
axis([-1 2 -1 5]);
pause;
end