u0'=-u0+(u1-u0)*d + k*u0/(1+uav^2)
u[1..49]'=-u[j]+(u[j+1]-2*u[j]+u[j-1])*d+k*u[j]/(1+uav^2)
u50'=-u50+(u49-u50)*d + k*u50/(1+uav^2)
uav=.02*sum(0,50)of(shift(u0,i'))
par d=1,k=3
done