Sharif Digital Repository

We study the following variant of the well-known line-simplification problem: we are getting a (possibly infinite) sequence of points p0,p1,p2,... in the plane defining a polygonal path, and as we receive the points, we wish to maintain a simplification of the path seen so far. We study this problem in a streaming setting, where we only have a limited amount of storage, so that we cannot store all the points. We analyze the competitive ratio of our algorithms, allowing resource augmentation: we let our algorithm maintain a simplification with 2k (internal) points and compare the error of our simplification to the error of the optimal simplification with k points. We obtain the algorithms... 

In this paper, the temperature of a moving surface is determined with a moving, finite element-based inverse method. In order to overcome the ill-condition of moving inverse problems, three different conventional regularization methods are used: Levenberg, Marquardt and Modified Levenberg. The moving mesh is generated employing the transfinite mapping technique. The proposed algorithms are used in the estimation of surface temperature on a moving boundary in the burning process of a homogenous solid fuel. The measurements obtained inside the solid media are used to circumvent problems associated with the sensor and the receding surface. As the surface recedes, the sensors are swept over by... 

Redundant signed digit number systems are popular in computationally intensive environments, particularly because of their carry-free property, which allows for digit-parallel addition. The time required for addition is particularly important because other arithmetic operations heavily depend on it. Signed digit number systems with high radices are of particular interest because of less memory requirement to represent a given number. But, the time required to perform digit-parallel addition is, by a relatively large coefficient, logarithmically proportional to the radix. Reduction of this coefficient is the prime goal of the study in this paper, where least cost implementations are... 

This work presents a method to find the exact solutions for the free vibration analysis of a delaminated beam based on the Timoshenko type with different boundary conditions. The solutions are obtained by the method of Lagrange multipliers in which the free vibration problem is posed as a constrained variational problem. The Legendre orthogonal polynomials are used as the beam eigenfunctions. Natural frequencies and mode shapes of various Timoshenko beams are presented to demonstrate the efficiency of the methodology  

Here a propeller design method based on a vortex lattice algorithm is developed, and two gradient-based and non-gradient-based optimization algorithms are implemented to optimize the shape and efficiency of two propellers. For the analysis of the hydrodynamic performance parameters, a vortex lattice method was used by implementing a computer code. In the first problem, one of the Sequential Unconstraint Minimization Techniques (SUMT) is employed to minimize the torque coefficient as an objective function, while keeping the thrust coefficient constant as a constraint. Also, chord distribution is considered as a design variable, namely 11 design variables. In the second problem, a modified... 

Clustering is the process of grouping data objects into set of disjoint classes called clusters so that objects within a class are highly similar with one another and dissimilar with the objects in other classes. The k-means algorithm is a simple and efficient algorithm that is widely used for data clustering. However, its performance depends on the initial state of centroids and may trap in local optima. In order to overcome local optima obstacles, a lot of studies have been done in clustering. The Fashion Algorithm is one effective method for searching problem space to find a near optimal solution. This paper presents a hybrid optimization algorithm based on Generalized Fashion Algorithm... 

Previous researches have shown the success of using reinforcement learning in solving combinatorial optimization problems. The main idea of these methods is to learn (near) optimal evaluation function to improve local searches and find (near) optimal solutions. Stage algorithm introduced by Boyan & Moore, is one of the most important algorithm in this area. In the other hand fuzzy methods have been used in all fields of science to solve problems but still never used in combinatorial optimization problems. In this paper we focus on Bin Packing Problem. We introduce two basic fuzzy algorithms (ALM and IDS) and then solve our problem with these fuzzy algorithms. We run ALM and IDS algorithms on... 

In this paper, a multi-item multiperiod inventory control problem with all-unit and/or incremental quantity discount policies under limited storage capacity is presented. The independent random demand rates of the items in the periods are known and the items are supplied in distinct batch sizes. The cost consists of ordering, holding, and purchasing. The objective is to find the optimal order quantities of all items in different periods such that the total inventory cost is minimized and the constraint is satisfied. A mixed binary integer programming model is first developed to model the problem. Then, a parameter-tuned genetic algorithm (GA) is employed to solve it. Since there is no... 

Recently, in many countries, power systems are moving towards creating a competitive structure for trading electrical energy. These changes, along with the numerous advantages of the Distributed Generators (DGs), have created more incentives for distribution companies to use these kinds of generators more than ever before. The Volt/Var control is one of the most important control schemes in distribution networks, which can be affected by DGs. This paper presents a new approach for the Volt/ Var control in distribution networks. The output reactive powers of the DGs, Static Var Compensators (SVCs), Load Tap Changers (LTCs) and the settings of the local controllers are chosen as the control... 

One of the categories of decoding techniques for DFT codes in erasure channels is the class of iterative algorithms. Iterative algorithms can be considered as kind of alternating mapping methods using the given information in a repetitive way. In this paper, we propose a new iterative method for decoding DFT codes. It will be shown that the proposed method outperforms the well-known methods such as Wiley/Marvasti, and ADPW methods in the decoding of DFT codes in erasure channels. © Springer-Verlag 2004  

In this paper, a new on-line handwritten signature verification system using Hidden Markov Model (HMM) is presented. The proposed system segments each signature based on its perceptually important points and then computes for each segment a number of features that are scale and displacement invariant. The resulted sequence is then used for training an HMM to achieve signature verification. Our database includes 622 genuine signatures and 1010 forgery signatures that were collected from a population of 69 human subjects. Our verification system has achieved a false acceptance rate (FAR) of 4% and a false rejection rate (FRR) of 12%. © 2003 IEEE  

The most common heart disease is Coronary artery disease (CAD). CAD is one of the main causes of heart attacks and deaths across the globe. Early diagnosis of this disease is therefore, of great importance. A large number of methods have thus far been devised for diagnosing CAD. Most of these techniques have been conducted on the basis of the Irvine dataset (University of California), which not only has a limited number of features but is also full of missing values and thus lacks reliability. The present study was designed to seek a new set, free from missing values, comprising features such as the functional class, dyspnea, Q wave, ST elevation, ST depression, and T inversion. Information... 

This paper reports the results of SIMD implementation of a number of interpolation algorithms on common personal computers. These methods fit a curve on some given input points for which a mathematical function form is not known. We have implemented four widely used methods using vector processing capabilities embedded in Pentium processors. By using SSE (streaming SIMD extension) we could perform all operations on four packed single-precision (32-bit) floating point values simultaneously. Therefore, the running time decreases three times or even more depending on the number of points and the interpolation method. We have implemented four interpolation methods using SSE technology then... 

This paper presents a new method for design of Variable Fractional Delay (VFD) FIR digital filters using Genetic Algorithm. In this method, each sub-filter of Farrow structure is designed separately with defined accuracy and bandwidth. Also, a variable mutation probability is employed, which improves the accuracy of the solution. Compared with exiting methods, it reduces the computational complexity and enhances the design flexibility. Sum-of-power-of-two (SOPOT) representation is applied to the filter coefficients. Therefore, SOPOT coefficients of Farrow structure are determined using a simple Genetic Algorithm without recourse to computational techniques. Using the SOPOT representation,... 

We study the impact of sub-array merging routines on merge-based sorting algorithms. More precisely, we focus on the galloping sub-routine that TimSort uses to merge monotonic (non-decreasing) sub-arrays, hereafter called runs, and on the impact on the number of element comparisons performed if one uses this sub-routine instead of a naive merging routine. The efficiency of TimSort and of similar sorting algorithms has often been explained by using the notion of runs and the associated run-length entropy. Here, we focus on the related notion of dual runs, which was introduced in the 1990s, and the associated dual run-length entropy. We prove, for this complexity measure, results that are... 

Color quantization is a technique for processing and reduction colors in image. The purposes of color quantization are displaying images on limited hardware, reduction use of storage media and accelerating image sending time. In this paper a hybrid algorithm of GA and Particle Swarm Optimization algorithms with FCM algorithm is proposed. Finally, some of color quantization algorithms are reviewed and compared with proposed algorithm. The results demonstrate Superior performance of proposed algorithm in comparison with other color quantization algorithms  

One of the main causes of death the world over are cardiovascular diseases, of which coronary artery disease (CAD) is a major type. This disease occurs when the diameter narrowing of one of the left anterior descending, left circumflex, or right coronary arteries is equal to or greater than 50 percent. Angiography is the principal diagnostic modality for the stenosis of heart vessels; however, because of its complications and costs, researchers are looking for alternative methods such as data mining. This study conducts data mining algorithms on the Z-Alizadeh Sani dataset which has been collected from 303 random visitors to Tehran's Shaheed Rajaei Cardiovascular, Medical and Research... 

Given a set S of n disjoint line segments in ℝ2, the visibility counting problem (VCP) is to preprocess S such that the number of segments in S visible from any query point p can be computed quickly. This problem can trivially be solved in logarithmic query time using O(n4) preprocessing time and space. Gudmundsson and Morin proposed a 2-approximation algorithm for this problem with a tradeoff between the space and the query time. They answer any query in Oε(n1−α) with Oε(n2+2α) of preprocessing time and space, where α is a constant 0 ≤ α ≤ 1, ε > 0 is another constant that can be made arbitrarily small, and Oε(f(n)) = O(f(n)nε). In this paper, we propose a randomized approximation algorithm... 

The anti-Ramsey numbers are a fundamental notion in graph theory, introduced in 1978, by Erdös, Simonovits and Sós. For given graphs G and H the anti-Ramsey number ar(G, H) is defined to be the maximum number k such that there exists an assignment of k colors to the edges of G in which every copy of H in G has at least two edges with the same color. Usually, combinatorists study extremal values of anti-Ramsey numbers for various classes of graphs. There are works on the computational complexity of the problem when H is a star. Along this line of research, we study the complexity of computing the anti-Ramsey number ar(G, Pk), where Pk is a path of length k. First, we observe that when k is...