Author: Miguel A. Ballicora
Date: 10:30:59 09/09/02
Go up one level in this thread
On September 09, 2002 at 03:13:09, José Carlos wrote: >On September 08, 2002 at 22:24:06, Miguel A. Ballicora wrote: > >>On September 08, 2002 at 21:17:47, José Carlos wrote: >> >>>On September 08, 2002 at 20:46:44, Miguel A. Ballicora wrote: >>> >>>>On September 07, 2002 at 11:13:20, Robert Hyatt wrote: >>>> >>>>> >>>>>Jose made a really good point about observed data vs measured data. After >>>>>thinking about it for a bit, I decided that it is a point strong enough to >>>>>change the way we think about "measured" and "observed". >>>>> >>>>>Some examples: >>>>> >>>>>speed. Impossible to measure. >>>>> >>>>>For example, your automobile (newer vehicles) compute speed by counting the >>>>>revolutions of the tailshaft (output) of the transmission, then factoring in >>>>>the rear-end ratio and the circumference of the rear wheels. It _computes_ >>>>>the speed from that. >>>>> >>>>>A radar measures the frequency change in a radio signal as it bounces off >>>>>a moving target and _computes_ the speed based on the frequency change. >>>>> >>>>>A GPS observes to "positions" in terms of lattitude and longitude, uses some >>>>>geometry to compute the distance between them, and uses a clock to measure the >>>>>time to cover that distance, and displays speed. >>>>> >>>>>So Speed can't be measured directly, it has to be computed. And this isn't a >>>>>surprise since speed is defined as distance over time. >>>>> >>>>>Brightness. (of a light, not a person. :) ) >>>>> >>>>>This is a direct measure of an electrical signal produced by some sort of >>>>>device (photo-resistor, photo-cell, optical transistor, etc) and then that >>>>>voltage is used to compute a brightness level in Lumens... >>>>> >>>>>Loudness (sound). >>>>> >>>>>Ditto. >>>>> >>>>>NPS. >>>>> >>>>>nodes searched divided by time in seconds. Computed. >>>>> >>>>>Speedup >>>>> >>>>>one-processor time divided by the N-processor time. Computed >>>>> >>>>>We really don't have a lot of "observed" data nowadays. Some, yes. Where >>>>>were you at 8pm last night. But more is computed... >>>>> >>>>>Which means if we start to define observed vs computed, we don't end up with >>>>>very much in the "observed" column. >>>>> >>>>>In a chess program I can count nodes and "compute" time (end-time minus >>>>>start-time) and then compute a nps value. I can measure run-time and compute >>>>>speed-up. But I can't directly measure speed at all. >>>> >>>>Not really, NPS is a direct measure. You do not measure nodes, you "report" >>>>them. In other words, there is no error in the measure of nodes. >>> >>> Not quite correct, IMO. Say you start iteration 11. You generate moves at the >>>root, then pick the first one. Go along the PV and go back in the tree. Let's >>>say you're in ply 6. So plies 1-5 are PV moves and from 6 on you have searched a >>>subtree. You test time and find you ran out, so you decide to stop searching. >>>Did you completely analyze the root node? I don't think so. You analyzed it >>>partially. Same for node in the PV until ply 5. >>> In parallel search there's something more. When you decide to stop the search >>>some processors might be generating moves, others might be evaluating, and so >>>on. >>> So "nodes searched" are not a discrete meause, thus they must be measured, not >>>just reported. >> >>They (nodes) might not mean what you really wanted to mean, but you define them >>and count them. For instance, number of times search is called or number of >>times makemove is called, whatever. You measure how long does it take to do a >>certain number of those events. Once those events are counted, they have no >>statistical error. If they do not represent what you want is a total different >>issue. >> >>Regards, >>Miguel > > Of course. I can define anything to make my life easier, but I guess that's >not the point. You can define speed as a constant (distance from Madrid to >Buenos Aires) divided by the time I need to do the travel, but that's not the >definition of speed, just a particular case. I was talking about the definition of nodes. You choose the definition, once you do it, you "count" them. > Also in a chess game, you don't do a search until some node count (whatever >the definition is) is hit and then stop. Your search decides _when_ to stop Yes I do :-) every 256 nodes I check the time. I never check what the time is unless I am in (nodes%256)==0. Except when a move was found, nodes are checked (reported) and then time is checked. I never check the time and then measure the nodes. I thought most of the people did it similarly. >based on time. So your node count is not constant. We could argue whether it is >a discrete measure or not, but certainly it's not constant. It is a discrete measure and because of that, no matter how you measure the nodes, the error is +/- 0 (unless there is a bug in the counter :-). In error propagation is treated as a constant, that was my point. Regards, Miguel > José C.
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