c	subroutine to do simpson intergration
	subroutine  simpn( a, b, ain )
	implicit  real*8 (a-h,p-z)
	real*8 a, b, f11, f22, dx, ai1, ai2, ain
	integer in,icount
	data derr /1.0e-4/
c	initilize
	in = ain
	dx = b - a
	icount = 0
	f11 = 0.0d0
	f22 = 0.0d0
	ia2 = 0.0d0
	f1 = funcn( a)
	f2 = funcn( b)
	fend = f1 + f2
 100	continue
	dx2 = dx
	dx = 0.5d0*dx
	x = a + dx
	f11 = 0.0d0
 200	continue
	f11 = f11 + funcn( x)
	x = x + dx2
	if  ( x .lt. b) go to 200
	ai1 = (fend + 2.0D0*f22 + 4.0D0*f11)*dx
	dai = ai2 - ai1
	ai2 = ai1
	icount = icount + 1
	f22 = f11 + f22
	if ( dabs(dai/ai2) .gt. derr .and .icount .le. 10) go to 100
	if ( icount .le. in)  go to 100
	ain = (ai2 - dai/15.0d0)/3.0d0
	return	
	end