FUNCTION ERFCX(X)
C     =================
C
C     complementary error function
C     expression from Abramowitz and Stegun, p.299, Eq. 7.1.26
C
      INCLUDE 'IMPLIC.FOR'
      PARAMETER (P  = 0.3275911D0,
     *           A1 = 0.254829592D0,
     *           A2 =-0.284496736D0,
     *           A3 = 1.421413741D0,
     *           A4 =-1.453152027D0,
     *           A5 = 1.061405429D0,
     *           UN = 1.D0)
      T=UN/(UN+P*X)
      ERFCX=0.
      IF(X.GT.13.) RETURN
      ERFCX=T*(A1+T*(A2+T*(A3+T*(A4+T*A5))))*EXP(-X*X)
      RETURN
      END