program schrodinger

c...... Solves the time-independent Schrodinger equation 
c...... for a potential box. Uses simple finite differences

c	by Dario Mitnik

	implicit real*8(a-h,o-z)


c....... initial values
	print*,' give the number of grid points'
	read*,npts
c.......   Potential Box
	print*,' give the size D of the potential box (-D/2 to D/2)'
	read*,d
	print*,' give the depth V0 of the potential well'
	read*,V0
c......... Initial Points
	print*,' give the initial value of the wavefunction P(0) '
	read*,p00
	print*,' give the initial value of the derivative at 0 Y(0) '
	read*,y00


100	open(unit=10,file='wave.dat',status='unknown')
	print*,' guess initial energy value'
	read*,Ener
	p0 = p00
	y0 = y00
	
c...... Other values
	dx = D/(2*npts)
c...... initial point P(1)
	p1 = p0 + dx*y0
	write(10,55) dx-dx,p0
	write(10,55) dx,p1
55	format(2(1x,1pg14.4))

c...... Solving the Schrodinger Equation
	do 200 i=2,npts*15
		V = V0
		if (i*dx.le.D/2) V = 0.0
		p = (2.0 + dx*dx*(V-Ener))*p1 - p0
		write(10,55) dx*i,p
		p0 = p1
		p1 = p
200	continue
		
	close(unit=10,status='keep')

	print*,' Continue?  No=0'
	read*,icont
	if (icont.ne.0) go to 100

	stop
	end