# Description of problem

I am trying to randomly perturb my network with an input at a given time point - I want to figure out how far my network has diverged from its initial trajectory (i.e. without the random input). In order to do this I need to keep track of the network dynamics following input and the network dynamics had I never perturbed the system.

However my network is stochastic due to poisson input so I can’t just re-run the network. What im wondering is if there is any feature in Brian to keep multiple instances of the exact same network (with the same stochastic input) dynamics, one where I add input and one where I dont?

2. snapshot the simulation with `store()` and go back to the earlier state with `restore` (see Running a simulation — Brian 2 2.4.2 documentation). You can ask `restore` to “rewind” the random number generator as well with the option `restore_random_state` (see restore function — Brian 2 2.4.2 documentation). The same comment as above holds – be careful that you ask for the same amount of random numbers in both cases.
The second option has the advantage that you only need to run the simulation once up to the point where you want to have the perturbation. On the downside, the `store`/`restore` mechanism does not work with the C++ standalone mode.