c harmonic oscillator classical case
real k ,mass
dimension xa(0:5000)
a(x)=-(k/mass)*x
xcero=1.
vcero=0.
xinicial=xcero
tscale=sqrt(mass/k)
omega=sqrt(k/mass)
nstep=2000
dt=6.5*tscale/float(nstep)
x1=vcero*dt+xcero
xa(0)=xcero
xa(1)=x1
do 10 i=2,nstep
x2