;routine to calculate coupling functions 
;here reduced to just one 
;Patrick Newell, JHU/APL November 13, 2006 

;calling routine supplies IMF bx, by, bz, v, n, and Ec 
;preferably after weighted average, such as inter_sol routine 
;return is coupling function Ec 
;density (n) is not actually used for this coupling function

pro sol_coup,bx,by,bz,v,n,Ec

Ec = 0.                          ;magic coupling function
  B = sqrt(bx*bx + by*by + bz*bz)
  if( (n*B*v) eq 0. )then begin
    return
  endif
  pi = 3.14159265
  BT = sqrt(by*by + bz*bz)
  bztemp = bz
  if( bz eq 0. ) then begin
      bztemp = 0.001
  endif
  tc = atan(by,bztemp)
  if( BT*cos(tc)*bz lt 0 ) then begin
       tc = tc + 3.14159265
   endif
  sintc = abs(sin(tc/2.))

Ec = (v^1.33333)*(sintc^2.66667)*(BT^0.66667)
return
end