function  velocity_new,energy,e=e,p=p,i=i

; To caluculate the velocity for electrons, protons and ions
;
;CREATED BY:	Linghua Wang
;LAST MODIFIED:	05/15/06

; energy in unit of eV

if keyword_set(e) then v=(sqrt(1.-(0.511d6/(0.511d6+energy))^2)*299792458.) ; for electron

if keyword_set(p) then v=(sqrt(1.-(931.49d6*1.007276/(931.49d6*1.007276+energy))^2)*299792458.) ; for proton

if keyword_set(i) then v=(sqrt(1.-(931.49d6/(931.49d6+energy))^2)*299792458.) ; for ion per amu

return,v ; m/s

end