FUNCTION pde,x
;
;  PDEs for geodesics.  The first 4 are the position, the last
;  4 are the directions.

; added common block "my_common"
; /Bo

  common my_common, M, a

  ;  Kerr BH with given M and a, returns metric and connection coeffs
  Kerr,x(1),x(2),x(3),g,cc,a=a,M=M ; added M=M, /Bo.

  ;  Accelerations, directions
  d2x = fltarr(4)
  dx  = x(4:7)
  dxx = dx#dx

  ;  Geodesic equation
  for i=0,3 do begin
    d2x(i) = -total(cc(i,*,*)*dxx) 
  end
;  print,x(1),x(3),total(g*dxx)

  ;  Return derivatives w.resp. to affine param.  Normalize with dt.
  return, [dx,d2x]/dx(0)

END