Journal:Informatica
Volume 14, Issue 2 (2003), pp. 167–180
Abstract
This work describes a realistic performance prediction tool for the parallel block LU factorization algorithm. It takes into account the computational workload, communication costs and the overlapping of communications by useful computations. Estimation of the tool parameters and benchmarking are also discussed. Using this tool we develop a simple heuristic for scheduling LU factorization tasks. Results of numerical experiments are presented.
Journal:Informatica
Volume 14, Issue 2 (2003), pp. 155–166
Abstract
A partially blind signature scheme allows the signer to inoculate a non‐removable common information into his blind signature. This common information may represent the date or the amount of e‐cash. Due to its un‐traceablility and partial blindness property, the partially blind signature plays an important role in many e‐commerce applications. Based on the RSA scheme, we propose a partially blind threshold signature with low‐computational load for the client.
Journal:Informatica
Volume 14, Issue 2 (2003), pp. 135–154
Abstract
Identifying legal and illegal states significantly reduces computational complexity of ATPG. A unified framework for identification of the legal and illegal states is presented. Most known methods for identification of the legal and illegal states are interpretable within this framework. New theorems and the resulting procedures for identifying exact collection of legal or illegal states of a circuit are presented. Experimental results demonstrate that exact collection of legal states for some circuits is significantly smaller than collections obtained by backward state search algorithm and by algorithm based on combinational ATPG theorems. The use of the exact collection of legal states allows identifying more undetectable faults. The proposed procedure for identifying of the exact collection of legal states starts from any state of the circuit, builds initially an enlarged collection of legal states and converges rapidly to the exact solution.
Journal:Informatica
Volume 14, Issue 1 (2003), pp. 121–130
Abstract
Recent publications on multidimensional scaling express contradicting opinion on multimodality of STRESS criterion. An example has been published with rigorously provable multimodality of STRESS. We present an example of data and the rigorous proof of multimodality of SSTRESS for this data. Some comments are included on widely accepted opinion that minimization of SSTRESS is easier than minimization of STRESS.
Journal:Informatica
Volume 14, Issue 1 (2003), pp. 111–120
Abstract
In the generalized group‐oriented cryptosystem, the sender can send a conditional message to a group of users such that only the specified sets of users in this group can cooperate to decrypt this message. In this paper, we will use an ElGamal cryptosystem and an elliptic curve ElGamal cryptosystem to achieve the purposes of generalization and group‐orientation, respectively. Both of our schemes are more efficient than Tsai et al.'s scheme in terms of sender's computational complexity.
Journal:Informatica
Volume 14, Issue 1 (2003), pp. 95–110
Abstract
It is a complex non‐linear problem to predict mechanical properties of concrete. As a new approach, the artificial neural networks can extract rules from data, but have difficulties with convergence by the traditional algorithms. The authors defined a new convex function of the grand total error and deduced a global optimization back‐propagation algorithm (GOBPA), which can solve the local minimum problem. For weights' adjustment and errors' computation of the neurons in various layers, a set of formulae are obtained by optimizing the grand total error function over a simple output space instead of a complicated weight space. Concrete strength simulated by neural networks accords with the data of the experiments on concrete, which demonstrates that this method is applicable to concrete properties' prediction meeting the required precision. Computation results show that GOBPA performs better than a linear regression analysis.
Journal:Informatica
Volume 14, Issue 1 (2003), pp. 85–94
Abstract
A group signature scheme is a digital signature scheme that allows a group member to sign messages anonymously on behalf of the group. Recently, Tseng and Jan proposed two group signature schemes based on self‐certified and ID‐based public keys respectively. However, these two schemes were shown to be insecure against forgery due to Joye et al. Later, Sun et al. showed that Tseng and Jan's self‐certified group signature scheme is linkable. In this paper, we first point out that the proposed linking equation, which is used to check the linkability of Tseng and Jan's self‐certified scheme, cannot work because the inverse problem of RSA is hard. A repaired linking equation is consequently proposed to fix this problem. Then, we show that Tseng and Jan's ID‐based scheme is still linkable because given any two valid group signatures it is easy to decide whether these two group signatures are generated by the same group member or not.
Journal:Informatica
Volume 14, Issue 1 (2003), pp. 75–84
Abstract
In this paper, the opening work on the development of a Lithuanian HMM speech recognition system is described. The triphone single‐Gaussian HMM speech recognition system based on Mel Frequency Cepstral Coefficients (MFCC) was developed using HTK toolkit. Hidden Markov model's parameters were estimated from phone‐level hand‐annotated Lithuanian speech corpus. The system was evaluated on a speaker‐independent ∼750 distinct isolated‐word recognition task. Though the speaker adaptation and language modeling techniques were not used, the system was performing at 20% word error rate.
Journal:Informatica
Volume 14, Issue 1 (2003), pp. 63–74
Abstract
The paper presents a technique that defines creation of ESTELLE/Ag specifications using knowledge bases (KB). Application KB is created using the knowledge acquisition technique joined with a piece‐linear aggregate model. The production rules of the application KB are transformed to decision tables, and the static properties of the KB are checked in PROLOGA system. Further, the application KB is combined with the defined KB of validated properties and validation method, and application KB dynamic properties are checked in the expert system in CLIPS. A validated application KB is used defining a framework of ESTELLE/Ag specification using PRAXIS editor and supplementing PRAXIS generated framework with the application functional description. The technique is illustrated with an example of a single channel queuing system.
Journal:Informatica
Volume 14, Issue 1 (2003), pp. 37–62
Abstract
The Markowitz model for single period portfolio optimization quantifies the problem by means of only two criteria: the mean, representing the expected outcome, and the risk, a scalar measure of the variability of outcomes. The classical Markowitz model uses the variance as the risk measure, thus resulting in a quadratic optimization problem. Following Sharpe's work on linear approximation to the mean‐variance model, many attempts have been made to linearize the portfolio optimization problem. There were introduced several alternative risk measures which are computationally attractive as (for discrete random variables) they result in solving Linear Programming (LP) problems. The LP solvability is very important for applications to real‐life financial decisions where the constructed portfolios have to meet numerous side constraints and take into account transaction costs. This paper provides a systematic overview of the LP solvable models with a wide discussion of their properties.