c----------------------------------------------------------------------
	function DERFX(x)
c  DERFX returns the value of the error function over x
c
c
c  author: Heiko Appel,  5.18.99, updated by Kieron, 8.15.99
c      in: x - argument for the error function
c     out: return value of function: value of error-function at x	
c   calls: --
	implicit real*8 (a-h,o-z)
	parameter(a=1.128379167095512573896158d0)