Lorenz '96 model

Lorenz/Emmanuel 1996 chaotic model usually used to test data assimilation systems.

X = lorenz4D(tf,F,pert)

In general, the Lorenz model is: (cyclical)
dX[j]/dt=(X[j+1]-X[j-2])*X[j-1]-X[j]+F
We use
J=40; %the number of variables
h=0.05; %the time step, equivalent to 6 hours

For the imput: tf is final time, F is the perturbation generally chosen to be 8 and pert is the perturbation (in the 20th variable) which is of the order of 10^-3.