# Why do the results differ when multiple dockings are done with the same input?

Up to table of contentsThis FAQ applies to: AutoDock 3, AutoDock 4

1. AutoDock uses a random number generator to create new poses for the ligand

during its search.

2. The random number generator used by AutoDock produces a sequence of random

numbers based on two initial seeds. The new conformations for the search are

created using this sequence of random numbers to set location, orientation and

torsion values.

3. The default values for these two seeds are 'pid' and 'time'. Process id

and time vary between AutoDock calculations.

4. Therefore, the sequence of random numbers is different between different

AutoDock calculations. As a result, the 'search' is encountering a different

set of random conformations. Thus the results differ.

Please note, it is possible to specify the seeds explicitly. In this case,

multiple AutoDock calculations should give the same, albeit restricted, results.

A separate consideration is that convergence of the docked results is an

indication of the thoroughness of the search. If the dockings in a single

AutoDock calculation vary greatly, possibly the the search hasn't been

thorough enough to find the minima in the energy landscape for a particular

docking problem. In this case, the search may need to be extended by

increasing the number of energy evaluations or the number of generations.