! 	  From: "COMPUTATIONAL PHYSICS 2nd Ed" 
! 		by RH Landau, MJ Paez, and CC Bordeianu 
! 		Copyright Wiley-VCH, 2007.
! 		Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
! 		MJ Paez, Univ Antioquia, 2007; and CC Bordeianu, Univ Bucharest, 2007.
! 		Supported by the US National Science Foundation															 
! 
! diff.f90: Forward, central and extrapolated differentiation 													
 		
Program diff

	Implicit none
  Real*8 :: f, h, result(3), x, xmin, xmax, xstep
	
	open(6, File = 'diff.dat', Status = 'Unknown')
	h			 = 1.e-5
	xmin	 = 0.0
	xmax	 = 7.0
	xstep = 0.01
	Do	x = xmin, xmax, xstep
	  result(1) = (f(x+h) - f(x))/h
		result(2) = (f(x+h/2) - f(x-h/2))/h
		result(3) = (8*(f(x+h/4)-f(x-h/4)) - (f(x+h/2)-f(x-h/2)))/(3*h)
		write (6, 20) x, result(1), result(2), result(3)
	End Do
20	Format(F5.3, TR4, F10.8, TR4, F10.8, TR4, F10.8) 
  close(6)		 
	Stop 'data saved in diff.dat'
End Program diff
                                              ! function to integrate
Function f(x)
  Implicit none
	Real*8 f, x
	f = cos(x)
	Return
End