Author: Robert Hyatt
Date: 21:21:06 09/08/02
Go up one level in this thread
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. > > José C. That is one issue. The one that burned me was that I used a real game to start the process. I don't complete iterations. If the search hits 12 plies and takes 3 minutes to produce the PV, but it searches another 2 minutes exactly, and reports 500,000,000 nodes. How many nodes to search the PV in that 3 minutes? Unknown. A good guess would be 3/5 * 500M = 300M. ANd that would definitely be very close. But measured? Hardly. Computed? Yes. Any better way to derive this? Not that I can see... > > >>What you really >>measure is the time to reach a certain number of "events" (in this case is >>nodes). Later, you make a conversion = [constant]/[time]. After a conversion, >>the measure does not become indirect because of the "calculation". You can >>measure inches an later you express them in cm. Still a direct measure. All the >>error depends on only one parameter measured. >> >>Miguel >> >>> >>>strange when you think about it... :)
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