program diffeqn3
C
C  illustrates elementary integration of a first-order
C  differential equation via explicit Euler scheme
C  and second-order taylor expansion
C  and implicit integration
C
C  CWJ SDSU April 2005
C
      implicit none

      real dt,t
      real x,y,z
 
      integer i,n

      print*,' Enter dx '
      read*,dt

      n = int(3./dt)

      x = 1.
      y = 1.
      z =1.

      do i = 0,n+1
         t=i*dt
         write(6,101)t,x,y,z,exp(-t*t/2.)
         x = x - dt*t*x
         y = y*(1.0-dt*t+0.5*dt*dt*(t*t-1))
         z =z*(1.-t*dt/2.)/(1+(t+dt)*dt/2.)
  101 format(f6.3,2x,4f10.5)

      enddo

      end