program leap ! Program to test numerical methods for integrating particle orbits in ! a magnetic field implicit none double precision vx0, vy0, vx1, vy1, vx2, vy2 double precision dt integer i vx0=1 ; vy0=0 ; dt=0.001 ! use 1st order Euler to start a leap from method vx1 = vx0 + dt*vy0 vy1 = vy0 - dt*vx0 do i=1,1000 vx2 = vx0 + 2*dt*vy1 vy2 = vy0 - 2*dt*vx1 vx0=vx1 vy0=vy1 vx1=vx2 vy1=vy2 enddo print *, "Energy = ", vx1**2+vy1**2 end program leap