Author: José Carlos
Date: 10:57:09 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. Mmm... Ok, in a sense, you're right. But I still object :) Let's see: as I understand (maybe I'm wrong on this) we want to calculate "nodes searched" not "nodes started to search". A searched node is: generated, searched the sub-tree and returned an evaluation back. When you stop the search (when you hit 256i nodes _started to search_) you haven't finished all of them. And still you return from the recursive calls with some flag to tell the root function "ignore this subtree" or something like that. My point is that some nodes were completed, some weren't. So your node count is just an optimistic estimation. But I accept this is too strict. In a parallel search you don't have an exact node count at all, though. >>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. Ok, that's fine. Time is also discrete then: clock ticks count. So nodes per second is a constant :) José C.
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