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ENTROPY(1) General Commands Manual ENTROPY(1)NAMEentropy - calculate data entropySYNOPSISentropy[-sv] [-tstring]DESCRIPTIONThis manual describes the operating procedure for theentropyprogram. This program will calculate the specific entropy for a given chunk of binary or ascii data that was previously read fromstdinor supplied on the command line via-t. The most common use for this program is to gauge the efficiency of a compression algorithm. In theory, based on the data's entropy, the max- imum theoretical compression rate can be calculated. To understand how compression works, we must understand that all data can be characterized by informational content, called itsentropy(the term is borrowed from Thermo-Dynamics). Compression is possible be- cause most data is represented with more bits then its entropy suggests is optimal.OPTIONS-tstringRather then read the data from thestdininput stream, use the stringstringas the source of the data. This is useful when you would like to calculate for a specific word or sen- tence.-sSorted output based on symbol frequencies-vPrint entropy version.THEORYA data set's entropy is the sum of each distinct symbol's entropies. A symbol is a distinct set of contiguous bits. For the sake of simplic- ity, I use 8 (number of bits making up a byte). It is important to note that a symbol doesNOThave to consist of 8 bits. A distinct symbols entropy `S' of symbol 'z' can be defined as:Sz=-log2(Pz)Where `Pz' is theprobabilityof symbol 'z' being found in the set. By storing each distinct symbol as a node in a list, we can calculate ex- actly how many times the symbol occurs in the set. This is also known as solving for the symbol'sfrequency. In order to calculate the overall entropy of the data; we sum the total entropies contributed by each distinct symbol and divide that by a co- efficient known as thedatasize. This coefficient is calculated by taking the number of bits per symbol and multiplying it by the total quantity of symbols.DIAGNOSTICSThe entropy utility exits 0 on success, and non-zero if an error oc- curs.SEE ALSOgzip(1), bzip2(1), tar(1), minigzip(1), gzexe(1), kgzip(8) compress(1), zcmp(1), zdiff(1), zlib(3)AUTHORo Chris S.J. PeronBUGSNone known. This does not mean they do not exist though. Please send bug reports and source code patches to (bugs@sqrt.ca). entropy version 1.0.0 9 Aug 2002 ENTROPY(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | THEORY | DIAGNOSTICS | SEE ALSO | AUTHOR | BUGS

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