function Back=upward(g)
% Calculated backward fraction of scattered radiation 
% g-asymetric parameter

Teta=[90:0.1:180];
PH=HGfun(Teta,g);
Tetaall=[0:0.1:180];
PHall=HGfun(Tetaall,g);
Back=trapz(cos(pi/180*Teta),PH)/trapz(cos(pi/180*Tetaall),PHall);
