function AddDottedLine(x,y,string,stringXfraction,stringYfraction)
% function AddDottedLine(x,y,string,stringXfraction,stringYfraction)
% adds horizontal and vertical dotted lines on existing plot.
% The string is placed at stringXfraction,stringYfraction by text2.
hold on; 
limits=axis;
plot([x x],[limits(3) y],'k:')
plot([limits(1) x],[y y],'k:')
text2(stringXfraction,stringYfraction,string)
hold off