[Camllist] entropy etc. in OCaml

Viktor Tron
 Markus Mottl
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Date:  20040811 (10:22) 
From:  Markus Mottl <markus@o...> 
Subject:  Re: [Camllist] entropy etc. in OCaml 
On Wed, 11 Aug 2004, Viktor Tron wrote: > Does anyone know of an OCaml library implementing or binding > Information Theoretical concepts like data entropy? > (e.g. gsl does not provide these). I don't have a separate library for that, but you might want to take a look at AIFAD: http://www.oefai.at/~markus/aifad It implements several functions for computing the entropy of discrete data including structured values. Its purpose is decision tree learning on structured data (represented by algebraic datatypes). One function for computing entropy from histograms is the following (taken from src/entropy_utils.ml in the distribution):  let calc_entropy histo n = if n = 0 then 0.0 else let rec loop sum ix = if ix < 0 then sum else let freq = histo.(ix) in if freq = 0 then loop sum (ix  1) else let ffreq = float freq in loop (sum +. ffreq *. log ffreq) (ix  1) in let sum = loop 0.0 (Array.length histo  1) in let f_n = float n in log2 f_n . sum /. f_n /. log_2  If you pass it an array of integers (histogram) that counts the frequency of class values in variable "histo" and the number of observations in "n" (must be the sum of frequencies in the histogram), then this function will return you the entropy in bits. Regards, Markus  Markus Mottl http://www.oefai.at/~markus markus@oefai.at  To unsubscribe, mail camllistrequest@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/camlbugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners