%
% opamp.m
%
% opamp(c,sc,flip)
%   c = [c(1) c(2)] center
%   sc = scale factor
%   flip = 0 (standard polarity)
%   flip = 1 (reversed polarity)
%
function opamp(c,sc,flip)
O = sc*[0 1 0 0
     0 -1/2 -1 0];
plot(c(1)+O(1,:),c(2)+O(2,:),'k','linewidth',1.5)
hold on
plot(c(1)+sc*[.1 .2],c(2)+sc*[-.3 -.3],'k','linewidth',2)  % minus sign
plot(c(1)+sc*[.15 .15],c(2)+sc*[-.25 -.35]-sc*flip*0.4,'k','linewidth',2)  % cross the minus
plot(c(1)+sc*[.1 .2],c(2)+sc*[-.7 -.7],'k','linewidth',2) % minus sign
return