tag:blogger.com,1999:blog-3722233.post110735211125671883..comments2024-11-13T15:38:29.005-06:00Comments on Computational Complexity: How to Judge a Weatherman?Lance Fortnowhttp://www.blogger.com/profile/06752030912874378610noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-3722233.post-1107499691479278572005-02-04T00:48:00.000-06:002005-02-04T00:48:00.000-06:00One nice things about logs is that uncertainty bec...One nice things about logs is that uncertainty becomes additive. For instance if your students were completely ignorant, and you replaced your 10 binary questions with 1 question having 1024 answers, they would still get the same number of points if using log p award scheme.<br /><br />Using log(p) as length for codeword of symbol with probability p is also guaranteed to produce lowest expected codeword length when codewords must be prefix-free (instantaneously decodable). I wonder, what sort of bounds would hold for codes without any such constraints?<br /><br />Finally, using f(x)=log x as a way to award points would elicit correct internal probabilities from rational students, whereas f(x)=x^2 will not. This seemed like an interesting topic, hence my first blog entry has a derivation of this :)<br />http://yaroslavvb.blogspot.com/Yaroslav Bulatovhttps://www.blogger.com/profile/06139256691290554110noreply@blogger.comtag:blogger.com,1999:blog-3722233.post-1107369882273560262005-02-02T12:44:00.000-06:002005-02-02T12:44:00.000-06:00It seems that both are correct.
Some weatherfore...It seems that both are correct. <br /><br />Some weatherforecasters use statistical data to search for other times where weather conditions were the same as today. In this case the probability is historical: in 20% of the days that were just like today it ended up raining.<br /><br />Others run a set of computer models or the same computer model with small variations (known as ensemble) and report the percentage of such outcomes. It rained in 20% of our computer simulations. Each outcome can be weighted to reflect the probability of a given variation.<br /><br />http://www.metoffice.com/research/nwp/publications/nwp_gazette/dec99/predict.html<br /><br />http://www.accuweather.com/adcbin/public/local_pop.asp?zipcode=02719&partner=sct<br /><br /><br />http://www.weatherzone.com.au/misc/glossary.jsp?letter=P<br />For instance, if the chance of receiving above-median rainfall in a particular climate scenario is 60%, then 60% of past years when that scenario occurred had above median rainfall, and 40% had below-median rainfall.<br /><br /><br />http://www.ucar.edu/research/tools/models.shtml<br />Because of weather's chaotic nature, errors or uncertainties in the starting point of a model can alter the results dramatically. One way to reduce the impact of such errors is through an ensemble of forecasts. In this technique, one model is run several times, each with a slightly different, intentionally varied set of starting points.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3722233.post-1107366632827705252005-02-02T11:50:00.000-06:002005-02-02T11:50:00.000-06:00This is old, but may shed some light on the issue:...This is old, but may shed some light on the issue:<br />http://www.straightdope.com/classics/a2_115b.htmlAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-3722233.post-1107360522834488792005-02-02T10:08:00.000-06:002005-02-02T10:08:00.000-06:00Back when the Usenet was popular, a recurring ques...Back when the Usenet was popular, a recurring question was "what do the weatherman probabilities mean?". This was well over a decade ago but I seem to recall that the answer was: the weather forecast service runs a few different computer models (usually 5 of them) and sees what is the outcome 24 hours into the future. If two models predict rain, then the probability is 40%, if 4 of them predict rain then it is 80%. <br /><br />At the risk of restarting a long dead usenet thread, can any one out there confirm this?Anonymousnoreply@blogger.com