% given a triangle (a,b,c) and a radius r, plot a circular arc
% of radius r centered at a that connected edges ab and ac
function plot_prop_arc_fill(a,b,c,ra,rb,rc)

angle0=imag(log(c-a));
angle1=imag(log((b-a)/(c-a) ));
angles=angle0+[0:.025:1]*angle1;
za=a+ra*exp(i*angles);

angle0=imag(log(a-b));
angle1=imag(log((c-b)/(a-b) ));
angles=angle0+[0:.025:1]*angle1;
zb=b+rb*exp(i*angles);

angle0=imag(log(b-c));
angle1=imag(log((a-c)/(b-c) ));
angles=angle0+[0:.025:1]*angle1;
zc=c+rc*exp(i*angles);

z=[za,zb,zc];
fill(real(z),imag(z),'c');
plot(real(za),imag(za),'k')
plot(real(zb),imag(zb),'k')
plot(real(zc),imag(zc),'k')
return