Author: José Carlos
Date: 00:13:09 09/09/02
Go up one level in this thread
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. 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 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. José C.
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