double precision pi, half
      double precision re, echarg, mc2pe, clsp
      double precision mc, mc2
      double complex im
      parameter ( pi= 3.14159265d0, half = 0.5d0 )
      parameter ( im = ( 0.0d0, 1.0d0 ) )
      parameter ( echarg = -1.602177d-19, clsp = 299792458.0d0 )
      parameter ( re = 2.817938d-15,  mc2pe = 511003.4d0 )
      parameter ( mc = 2.730969732d-22,  mc2 = 8.187241286d-14 )
c