history of BMZ algorithm is available
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BMZ.t2t
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BMZ.t2t
@ -4,15 +4,48 @@ BMZ Algorithm
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%!includeconf: CONFIG.t2t
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%!includeconf: CONFIG.t2t
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**History**
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**History**
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At the end of 2003, professor [Nivio Ziviani http://www.dcc.ufmg.br/~nivio] was
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finishing the second edition of his book.
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During the book writing, professor Nivio studied the problem of generating minimal perfect hash
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functions (if you are not familiarized with this problem, see [1][2]).
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Professor Nivio coded a modified version of the [CHM algorithm chm.html], which was proposed by
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Czech, Havas and Majewski and put it in his book.
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The [CHM algorithm chm.html] is based on acyclic random graphs to generate order preserving
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minimal perfect hash functions in linear time. Professor Nivio argued himself, why must the random graph
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be acyclic? In the modified version availalbe in his book he got rid of such restriction.
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The modification presented a problem, it was impossible to generate minimal perfect hash functions
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for sets with more than 1000 keys.
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At the same time, [Fabiano C. Botelho http://www.dcc.ufmg.br/~fbotelho],
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a master degree student at [Departament of Computer Science http://www.dcc.ufmg.br] in
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[Federal University of Minas Gerais http://www.ufmg.br],
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started to be advised by Nivio who presented the problem to Fabiano.
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During the master, Fabiano and Nivio faced lots of problems.
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Talking with a friend of mine (David Menoti) about our problems, many ideas
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appeared and after of implementing them, we got a very fast algorithm to generate
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minimal perfect hash functions that does not preserve order.
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We refer the algorithm to as **BMZ**, because it was conceived by Fabiano C. **B**otelho
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David **M**enoti and Nivio **Z**iviani. The algorithm is described in [1].
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To analyse BMZ algorithm we needed some results from the random graph theory, so
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we invite professor [Yoshiharu Kohayakawa http://www.ime.usp.br/~yoshi] to help us.
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The final description and analysis of BMZ algorithm is presented in [2].
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**The Algorithm**
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**The Algorithm**
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**The Heuristic**
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**The Heuristic**
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**Papers**
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**Papers**
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+ [F. C. Botelho http://www.dcc.ufmg.br/~fbotelho], D. Menoti, [N. Ziviani http://www.dcc.ufmg.br/~nivio]. [A New algorithm for constructing minimal perfect hash functions papers/bmz_tr004_04.ps], Technical Report TR004/04, Department of Computer Science, Federal University of Minas Gerais, 2004.
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+ [F. C. Botelho http://www.dcc.ufmg.br/~fbotelho], Y. Kohayakawa, and [N. Ziviani http://www.dcc.ufmg.br/~nivio]. [A Practical Minimal Perfect Hashing Method papers/bmz_wea2005.ps], 4th International Workshop on Efficient and Experimental Algorithms (WEA), 2005.(submitted)
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[Home index.html]
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[Home index.html]
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Before Width: | Height: | Size: 271 B After Width: | Height: | Size: 2.6 KiB |
9
CHM.t2t
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CHM.t2t
@ -11,6 +11,15 @@ CHM Algorithm
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**Papers**
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**Papers**
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+ Z.J. Czech, G. Havas, and B.S. Majewski. [An optimal algorithm for generating minimal perfect hash functions. papers/chm92.pdf], Information Processing Letters, 43(5):257-264, 1992.
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+ Z.J. Czech, G. Havas, and B.S. Majewski. Fundamental study perfect hashing.
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Theoretical Computer Science, 182:1-143, 1997.
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+ B.S. Majewski, N.C. Wormald, G. Havas, and Z.J. Czech. A family of perfect hashing methods.
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The Computer Journal, 39(6):547--554, 1996.
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[Home index.html]
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[Home index.html]
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9
FAQ.t2t
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FAQ.t2t
@ -8,7 +8,7 @@ CMPH FAQ
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perfect hash function, the ids will be the indices of the keys in the
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perfect hash function, the ids will be the indices of the keys in the
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input. Otherwise, you have no guarantee of the distribution of the ids.
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input. Otherwise, you have no guarantee of the distribution of the ids.
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- Why I always get the error "Unable to create minimum perfect hashing function"?
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- Why do I always get the error "Unable to create minimum perfect hashing function"?
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- The algorithms do not guarantee that a minimal perfect hash function can
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- The algorithms do not guarantee that a minimal perfect hash function can
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be created. In practice, it will always work if your input
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be created. In practice, it will always work if your input
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is big enough (>100 keys).
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is big enough (>100 keys).
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@ -18,6 +18,13 @@ CMPH FAQ
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``` #sort input.txt | uniq > input_uniq.txt
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``` #sort input.txt | uniq > input_uniq.txt
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and run cmph with input_uniq.txt
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and run cmph with input_uniq.txt
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- Why do I change the hash function using cmph_config_set_hashfuncs function and the default (jenkins)
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one is executed?
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- Probably you are you using the cmph_config_set_algo function after
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the cmph_config_set_hashfuncs. Therefore, the default hash function
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is reset when you call the cmph_config_set_algo function.
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[Home index.html]
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[Home index.html]
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