Date: Mon, 13 Aug 2001 00:17:47 -0700 (PDT) From: Ranjit Nair To: RoboCup Rescue English ML Subject: Ensuring the repeatability of the simulation Hi, I would like to begin the discussion of the issue of ensuring repeatability of the system. There are several possible reasons for the lack of repeatability of current simulation. It would be useful to list these and determine which of these are really the cause of the problem. 1. Random variables in simulators: The random variables in the simulators were identified and the values of the seeds were set. This should ensure that multiple runs give the same results. However, it is possible that random variables were inadvertently left out in some simulation component. 2. Packets getting lost: It seemed to me that some of the packets especially when the simulation just begins could be getting lost. Thus for example, if the agent issues a command to move itself out of a building and this packet gets lost, the agent could remain stuck in the building and could die. I suspect that the contents of the memory pool of each simulator component is not the same because of this initial loss of packets and thus they each simulate the world according to what they believe to be true. This could be easily checked. 3. Packets arriving out of order: The order that the packets arrive make a difference since the simulation is not commutative. Possible soluions: 1. A shared memory structure that is used by kernel and all simulators for memory. 2. Using TCP/IP for communication: Could affect real-time behavior of simulation. 3. Each simulator on a different socket with the kernel receving from and sending to them in a fixed order. Temporary solution: 1. Change the step time from 1000 milliseconds to some larger number in the config file. This might reduce the amount of packet loss. Regards, Ranjit Ranjit Nair Graduate Research Assistant Computer Science Department University of Southern California Off Phone: (213) 740 6747 Web Page: www.isi.edu/~nair/ ---------------------------------------------------------- |Artificial Intelligence is no match for Natural Stupidity.| ----------------------------------------------------------