%
% summer
%
source([0 0],'V_1','h');
resist([3 0],'h','R_1','y_1')

source([0 -3],'V_2','h');
resist([3 -3],'h','R_2','y_2')

source([0 -6],'V_3','h');
resist([3 -6],'h','R_3','y_3')

source([0 -9],'V_4','h');
resist([3 -9],'h','R_4','y_4')

plot([6.6 6.6],[0 -10],'k','linewidth',1.5)
plot([0 0],[0 -11],'k','linewidth',1.5)
ground([0 -11],'')

opamp([12 -4],4,0)

resist([6.6 -10],'v','R_5','y_5'); ground([6.6 -13.6],'')
resist([10 -10],'v','R_6','y_6'); ground([10 -13.6],'')
plot([10 10],[-7 -10],'k','linewidth',1.5)
plot([10 12],[-7 -7],'k','linewidth',1.5)
plot([6.6 12],[-5 -5],'k','linewidth',1.5)

resist([12 -9],'h','R_7','y_7'); 
plot([10 12],[-9 -9],'k','linewidth',1.5)
plot([15.6 17],[-9 -9],'k','linewidth',1.5)
plot([17 17],[-9 -6],'k','linewidth',1.5)
plot([16 17],[-6 -6],'k','linewidth',1.5)

text(7,-4.5,'x_1')
text(10.5,-8.5,'x_1')
text(16,-8.5,'x_2')

axis off
hold off
return