Author: Keith Evans
Date: 16:37:46 09/07/02
Go up one level in this thread
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. A GPS measures pseudo-ranges and uses these to compute position based upon the positions of the satellites. The satellites broadcast their ephemeris data, or with A-GPS you get it from a server. (You have to know or search for the doppler too just to be able to mesaure the pseudo-ranges.) Nav guys like to use a Kalman filter as part of the position solution - they may actually get the velocity out of the Kalman filter, but I'm not a nav guy. Anyways the GPS position isn't measured directly either. In GPS you use phrases like "< xxx meter circular error probability", "probability of detection", "probability of false alarms",... I wanted to keep this short since it's pretty off topic. >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. > >strange when you think about it... :)
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.