! 	  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							
! 
! 	 eqheat.f90: Solution of heat equation using with finite diffs
 																														
Program heat

  Implicit none				
	Double precision :: cons, ro, sph, thk, u(101, 2)
	Integer :: i, k, max
	
	open(9, FILE = 'eqheat.dat', Status = 'Unknown')
	sph = 0.113                                    ! specific heat iron
	thk = 0.12                             !  thermal conductivity iron
	ro = 7.8                                         ! density for iron
	cons  =  thk/(sph*ro)
  max = 30000                                  ! number of iterations
                                         ! t = 0, all points at 100 C
	Do	i = 1, 100
	  u(i, 1) = 100.0
	End Do
  Do	i = 1, 2                                ! Endpoints always zero
	  u(1, i)	 = 0.0
		u(101, i) = 0.0
	End Do                                                
	                                                   ! loop over time
	Do	k = 1, max                                           
                                                    ! loop over space
	  Do	i = 2, 100                                        
		  u(i, 2) = u(i, 1) + cons*(u(i+ 1, 1) + u(i- 1, 1) - 2*u(i, 1))
		End Do
		If ( (Mod(k, 1000) == 0) .or. (k == 1) ) then  ! every 1000 steps
		  Do	i = 1, 101, 2
			  write(9, 22) u(i, 2)
		  End Do
			Write (9, 22)
			EndIf
			                                           ! new values - > old
			Do	i = 2, 100                                   
			  u(i, 1) = u(i, 2)
			End Do
	End Do
 22	format (f10.6)
	close(9)
	Stop 'data saved in eqheat.dat (for gnuplot)'
End Program heat