Author: Robert Hyatt
Date: 11:08:25 09/09/02
Go up one level in this thread
On September 09, 2002 at 13:30:59, Miguel A. Ballicora wrote: >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. The problem is _you_ check the time every 256 nodes. Doesn't mean the O/S _updates_ the time that often. In fact, on PC machines it certainly does not. And about the best accuracy you get today is 10 milliseconds +/-... And that not on a PC > >>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 If there is no error then you can reproduce it, correct? Then we have _another_ problem with SMP nodes... > > >> José C.
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.