Jiri Dvorský

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In this article we discuss a simple hash function based upon properties of a well-known combinatorial design called quasigroups. The quasigroups are equivalent to the more familiar Latin squares and one of their most important properties is that all possible element of certain quasigroup occurs with equal probability. Actual implementations are based on(More)
In this study we discuss a method for evolution of quasigroups with desired properties based on genetic algorithms. Quasigroups are a well-known combinatorial design equivalent to the more familiar Latin squares. One of their most important properties is that all possible elements of certain quasigroup occur with equal probability. The quasigroups are(More)
Approach based on clustering will be described in our paper. Basic version of our system was given in [5] allows us to expand query through special index. Hierarchical agglomerative clustering of the whole document collection generates the index. Retrieving of topic development is specific problem. Standard methods of IR does not allow us such kind of(More)
Genetic algorithms have been successfully used for searching for quasigroups with good properties. In this study we extend previous work done on evolutionary search for quasigroups by defining new fitness functions based on selected algebraical properties of the quasigroups. Introduced fitness functions make use of heterogeneous sequences generated during(More)
In this article we present a new compression method, called WLZW, which is a word-based modiication of classic LZW. The modiication is similar to the approach used in the HuuWord compression algorithm. The algorithm is two-phase, the compression ratio achieved is fairly good, on average 22%-20% (see 2, 3]). Moreover, the table of words, which is side(More)
The paper is oriented to the problem of clustering for large datasets with high-dimensions. We propose a two-phase combined method with regard to high dimensions and exploiting the standard clustering algorithm. The first step of the method is based on the learning phase using artificial neural network, especially Self organizing map, which we find as a(More)
Quasigroups are a well-known combinatorial design equivalent to more familiar Latin squares. Since all possible elements of a quasigroup occur with equal probability, it could be an interesting tool for information assurance and network security. Most of the previous implementations of quasigroups were based on look-up table of the quasigroup, on system of(More)
Quasigroups are a well-known combinatorial design equivalent to more familiar Latin squares. Because all possible elements of a quasigroup occur with equal probability, it makes it an interesting tool for the application in computer security and for production of pseudorandom sequences. Most implementations of quasigroups are based on look-up table of the(More)
N-grams are applied in some applications searching in text documents, especially in cases when one must work with phrases, e.g. in plagiarism detection. N-gram is a sequence of n terms (or generally tokens) from a document. We get a set of n-grams by moving a floating window from the begin to the end of the document. During the extraction we must remove(More)