;+ ;FUNCTION: velocity(energy,mass) ;PURPOSE: ; Returns the relativistic momentum over mass given the energy and mass ; ;- function velocity,nrg,mass,true_veloc=tv,momen_on_mass=mom, $ electron=el,proton=proton,inverse=inverse c2 = 2.99792d5^2 if keyword_set(el) then mass= 511000.d/c2 if keyword_set(proton) then mass= 511000.d/c2*1836. E0 = mass*c2 if keyword_set(tv) then begin gamma = (nrg+e0)/e0 vmag = sqrt((1.-1./gamma^2)*c2) if keyword_set(inverse) then message,'not working!' return,vmag endif if 1 then begin ; momentum over mass if keyword_set(inverse) then begin vel= nrg return, e0 * (sqrt(1+(vel^2/c2))-1) endif vmag = sqrt(2*nrg/mass * (1 +nrg/2/e0)) return ,vmag endif end