Search for: computational-complexity
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    A memory efficient algorithm for multi-dimensional wavelet transform based on lifting

    , Article 2003 IEEE International Conference on Accoustics, Speech, and Signal Processing, Hong Kong, 6 April 2003 through 10 April 2003 ; Volume 6 , 2003 , Pages 401-404 ; 15206149 (ISSN) Taghavi, Z ; Kasaei, S ; Sharif University of Technology
    Conventional implementation of multi-dimensional wavelet transform (e.g. 3-D wavelet) requires whether a high amount of "in access" memory or a continual access to slow memory of a processor which makes it infeasible for most applications. In this paper, we proposed a novel algorithm for computation of an n-D discrete wavelet transform (DWT) based on lifting scheme. In addition to benefits of lifting scheme (which causes a major reduction in computational complexity and performs the total computations in time domain), our real-time approach computes the coefficients for all kinds of 1st and 2 nd generation wavelets with short delay and optimized utilization of the slow and fast memories of a... 

    A new efficient PNLMS based algorithm for adaptive line echo cancellation

    , Article 7th International Symposium on Signal Processing and Its Applications, ISSPA 2003, Paris, 1 July 2003 through 4 July 2003 ; Volume 2 , 2003 , Pages 555-558 ; 0780379462 (ISBN); 9780780379466 (ISBN) Maleki, A ; Nayebi, K ; Sharif University of Technology
    IEEE Computer Society  2003
    Echo cancellers with long impulse responses are usually used in networks with long echoes. Since long adaptive filters with sparse target filters usually converge very slowly, adaptation algorithms with fast convergence rate are needed. PNLMS [2] is one of the algorithms that is designed for fast convergence on sparse impulse responses. But there are some disadvantages to this algorithm. The computational complexity of this algorithm is prohibitive, especially for long echo tails. Another disadvantage is that its convergence rate slows down significantly after the adaptation of large taps. In this paper we propose new algorithms to solve both these problems. In another part of this paper, we... 

    On the complexity of isoperimetric problems on trees [electronic resource]

    , Article Discrete Applied Mathematics ; Volume 160 Issue 1-2, January, 2012 Pages 116-131 Daneshgar, A. (Amir) ; Javadi, Ramin ; Sharif Univercity of Technology
    This paper is aimed at investigating some computational aspects of different isoperimetric problems on weighted trees. In this regard, we consider different connectivity parameters called minimum normalized cuts/isoperimetric numbers defined through taking the minimum of the maximum or the mean of the normalized outgoing flows from a set of subdomains of vertices, where these subdomains constitute a partition/subpartition. We show that the decision problem for the case of taking k-partitions and the maximum (called the max normalized cut problem NCP^M), and the other two decision problems for the mean version (referred to as IPP^m and NCP^m) are NP-complete problems for weighted trees. On... 

    On the Complexity of Deciding Whether the Regular Number is at Most Two

    , Article Graphs and Combinatorics ; Volume 31, Issue 5 , September , 2014 , pp 1359-1365 ; ISSN: 09110119 Dehghan, A ; Sadeghi, M. R ; Ahadi, A ; Sharif University of Technology
    The regular number of a graph (Formula presented.) denoted by (Formula presented.) is the minimum number of subsets into which the edge set of (Formula presented.) can be partitioned so that the subgraph induced by each subset is regular. In this work we answer to the problem posed as an open problem in Ganesan et al. (J Discrete Math Sci Cryptogr 15(2-3):49-157, 2012) about the complexity of determining the regular number of graphs. We show that computation of the regular number for connected bipartite graphs is NP-hard. Furthermore, we show that, determining whether (Formula presented.) for a given connected (Formula presented.)-colorable graph (Formula presented.) is NP-complete. Also, we... 

    Design and implementation of extended predictive functional control for boiler-turbine unit of power plant

    , Article 24th Mediterranean Conference on Control and Automation, 21 June 2016 through 24 June 2016 ; 2016 , Pages 131-134 ; 9781467383455 (ISBN) Amirabadi Farahani, M ; Haeri, M ; MCA ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    In this paper, a new model predictive controller is introduced to control a power unit process with three inputs and three outputs. This method is proposed to reduce the complexity of the required computation. In fact, the presented controller ensures achieving an acceptable performance in the presence of noise and disturbances and reduces the volume of calculations to control a complex and nonlinear boilerturbine process. The simulation results indicate that the implementation of the proposed controller requires less computing time while the performance degradation is not more than five percent  

    Optimal point removal in closed-2PM labeling

    , Article Information Processing Letters ; Volume 105, Issue 3 , 2008 , Pages 108-113 ; 00200190 (ISSN) Rostamabadi, F ; Sadeghi, I ; Ghodsi, M ; Khosravi, R ; Sharif University of Technology
    An optimal labeling where labels are disjoint axis-parallel equal-size squares is called 2PM labeling if the labels have maximum length each attached to its corresponding point on the middle of one of its horizontal edges. In a closed-2PM labeling, no two edges of labels containing points should intersect. Removing one point and its label, makes free room for its adjacent labels and may cause a global label expansion. In this paper, we construct several data structures in the preprocessing stage, so that any point removal event is handled efficiently. We present an algorithm which decides in O (lg n) amortized time whether a label removal leads to label expansion in which case a new optimal... 

    Spanning trees with minimum weighted degrees

    , Article Information Processing Letters ; Volume 104, Issue 3 , 2007 , Pages 113-116 ; 00200190 (ISSN) Ghodsi, M ; Mahini, H ; Mirjalali, K ; Oveis Gharan, S ; Sayedi Roshkhar, A. S ; Zadimoghaddam, M ; Sharif University of Technology
    Given a metric graph G, we are concerned with finding a spanning tree of G where the maximum weighted degree of its vertices is minimum. In a metric graph (or its spanning tree), the weighted degree of a vertex is defined as the sum of the weights of its incident edges. In this paper, we propose a 4.5-approximation algorithm for this problem. We also prove it is NP-hard to approximate this problem within a 2 - ε factor. © 2007 Elsevier B.V. All rights reserved  

    A new learning algorithm for the MAXQ hierarchical reinforcement learning method

    , Article ICICT 2007: International Conference on Information and Communication Technology, Dhaka, 7 March 2007 through 9 March 2007 ; 2007 , Pages 105-108 ; 9843233948 (ISBN); 9789843233943 (ISBN) Mirzazadeh, F ; Behsaz, B ; Beigy, H ; Sharif University of Technology
    The MAXQ hierarchical reinforcement learning method is computationally expensive in applications with deep hierarchy. In this paper, we propose a new learning algorithm for MAXQ method to address the open problem of reducing its computational complexity. While the computational cost of the algorithm is considerably decreased, the required storage of new algorithm is less than two times as the original learning algorithm requires storage. Our experimental results in the simple Taxi Domain Problem show satisfactory behavior of the new algorithm  

    New relations and separations of conjectures about incompleteness in the finite domain

    , Article Journal of Symbolic Logic ; November , 2021 ; 00224812 (ISSN) Khaniki, E ; Sharif University of Technology
    Cambridge University Press  2021
    In [20] Kraj´ıˇcek and Pudl´ak discovered connections between problems in computational complexity and the lengths of first-order proofs of finite consistency statements. Later Pudl´ak [25] studied more statements that connect provability with computational complexity and conjectured that they are true. All these conjectures are at least as strong as P ̸= NP [23, 25, 24]. One of the problems concerning these conjectures is to find out how tightly they are connected with statements about computational complexity classes. Results of this kind had been proved in [20, 22]. In this paper, we generalize and strengthen these results. Another question that we address concerns the dependence between... 

    An effective approach for dynamic analysis of rovers

    , Article Robotica ; Volume 23, Issue 6 , 2005 , Pages 771-780 ; 02635747 (ISSN) Meghdari, A ; Karimi, R ; Pishkenari, H. N ; Gaskarimahalle, A. L ; Mahboobi, S. H ; Sharif University of Technology
    In this paper a novel approach to dynamic formulation of rovers has been presented. The complexity of these multi-body systems especially on rough terrain, challenged us to use the Kane's method which has been preferred to others in these cases. As an example, symbolic equations of a six-wheeled rover, named CEDRA Rescue Robot which uses a shrimp like mechanism, have been derived and a simulation of forward and inverse dynamics has been presented. Due to the clear form of equations, each term defines a physical meaning which represents the effect of each parameter, resulting in a frame-work for performance comparison of rovers. Although the method has been described for a 2-D non-slipping... 

    Design of variable fractional delay FIR filters using genetic algorithm

    , Article 2003 10th IEEE International Conference on Electronics, Circuits and Systems, ICECS2003, Sharjah, 14 December 2003 through 17 December 2003 ; Volume 1 , 2003 , Pages 48-51 ; 0780381637 (ISBN); 9780780381636 (ISBN) Khamei, K ; Nabavi, A ; Hessabi, S ; Sharif University of Technology
    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,... 

    A genetic approach in relay-jammer selection and power allocation for physical layer security

    , Article 8th International Symposium on Telecommunications, IST 2016, 27 September 2016 through 29 September 2016 ; 2017 , Pages 374-379 ; 9781509034345 (ISBN) Okati, N ; Mosavi, M. R ; Behroozi, H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Node cooperation approaches improve physical layer security in wireless networks without applying data encryption. Selecting the appropriate nodes to cooperate as relays or friendly jammers, to degrade eavesdropper's link, is a challenging problem which has attracted a lot of attention in recent years. Various approaches, based on conventional exhaustive search, have been suggested for optimal relay-jammer selection and power allocation in the literature. The complexity of these methods is proportional to the number of intermediate nodes. As the number of intermediate nodes exceeds a specific bound, conventional exhaustive search appears infeasible due to high computational complexity. In... 

    Computational complexity of wavelength-based machine with slightly interacting sets

    , Article International Journal of Unconventional Computing ; Volume 13, Issue 2 , 2017 , Pages 117-137 ; 15487199 (ISSN) Goliaei, S ; Foroughmand Araabi, M. H ; Sharif University of Technology
    Old City Publishing  2017
    The wavelength-based machine is a computational model working with light and optical devices. Wavelength-Based machine assumes that it can breakdown light to several very small pieces and act on them simultaneously to achieve efficiency in computation. In this paper, first we introduce the wavelength-based machine. Then, we define two new operations: concentration and double concentration operations, which give the wavelength-based machine the ability to check the emptiness of one and two light rays. Both of the concentration and double concentration operations are implemented by white-black imaging systems. In this paper, we compare the computational power of P-uniform wavelength-based... 

    Separating radar signals from impulsive noise using atomic norm minimization

    , Article IEEE Transactions on Circuits and Systems II: Express Briefs ; Volume 68, Issue 6 , 2021 , Pages 2212-2216 ; 15497747 (ISSN) Bayat, S ; Daei, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    We consider the problem of corrupted radar super-resolution, a generalization of compressed radar super-resolution in which one aims to recover the continuous-valued delay-Doppler pairs of moving objects from a collection of corrupted and noisy measurements. The received signal in this type consists of contributions from objects, outlier and noise. While this problem is ill-posed in general, tractable recovery is possible when both the number of objects and corrupted measurements are limited. In this brief, we propose an atomic norm optimization in order to find the delay-Doppler pairs and the outlier signal. The objective function of our optimization problem encourages both sparsity in the... 

    Some Results and Conjectures on Bounds for Graph Colorings

    , M.Sc. Thesis Sharif University of Technology Dehghan, Ali (Author) ; Mahmoodian, Ebadollah (Supervisor)
    There are many ways to color the vertices and edges of graphs, such as, rainbow connection, vertex coloring and dynamic coloring. In this thesis, in Chapter 1 we introduce a new coloring, we consider its relationship with some other colorings and we investigate its computational complexity. In chapter 1, we focus on the proper orientation number. The problem of orienting the edges of a given simple graph so that the maximum indegree of vertices is minimized was introduced in 2004. We show that there is a polynomial time algorithm for determining the proper orientation number of a given 3-regular graph. But it is NP-complete to decide if the proper orientation number of a 4-regular graph is 3... 

    Dichotomy and Polymorphisms

    , M.Sc. Thesis Sharif University of Technology Yasaee Meybodi, Fatemeh (Author) ; Daneshgar, Amir (Supervisor)
    In general, Constrain Satisfaction Problems (CSP’s) are NP-complete, however, this is not the case, if we impose some restrictions on the constraints. Due to importance and applications of CSP’s in different areas of engineering and science including artificial intelligence, relational databases and logic, investigating the computational complexity of CSP’s is an important issue. Computational complexity of CSP’s has been investigated from a variety of aspects, including the Universal Algebraic approach that has given rise to a solution of dichotomy conjecture recently. In this thesis based on contributions of Bulatov, Krokhin and Jeavons, we try to explain this universal algebraic approach... 

    Descriptive Complexity for Counting Problems

    , M.Sc. Thesis Sharif University of Technology Yaghoubi, Omid (Author) ; Ebrahimi Boroojeni, Javad (Supervisor)
    Descriptive complexity refers to the difficulty of expressing a problem in a formal language, allowing for a complete and precise description of the problem, including output specifications for function problems. Despite the success of the descriptive approach in computational complexity, this approach has been predominantly used for decision problems. In contrast to decision problems, a counting problem can be considered as a function with the range of natural numbers. This thesis focuses on the examination of counting problems from a descriptive perspective, exploring the connection between their descriptive and computational versions. Toward this goal, weighted logic is utilized to... 

    Computation of lucky number of planar graphs is NP-hard

    , Article Information Processing Letters ; Volume 112, Issue 4 , February , 2012 , Pages 109-112 ; 00200190 (ISSN) Ahadi, A ; Dehghan, A ; Kazemi, M ; Mollaahmadi, E ; Sharif University of Technology
    A lucky labeling of a graph G is a function l:V(G)→N, such that for every two adjacent vertices v and u of G, σ w∼vl(w)≠ σ w∼ul(w) (x∼y means that x is joined to y). A lucky number of G, denoted by η(G), is the minimum number k such that G has a lucky labeling l:V(G)→{1,⋯,k}. We prove that for a given planar 3-colorable graph G determining whether η(G)=2 is NP-complete. Also for every k≥2, it is NP-complete to decide whether η(G)=k for a given graph G  

    An invertible quantization based watermarking approach

    , Article 2008 IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP, Las Vegas, NV, 31 March 2008 through 4 April 2008 ; 2008 , Pages 1677-1680 ; 15206149 (ISSN) ; 1424414849 (ISBN); 9781424414840 (ISBN) Saberian, M. J ; Akhaee, M. A ; Marvasti, F ; Sharif University of Technology
    In this paper a new class of invertible watermarking approach based on quantization has been introduced. Based on the necessary conditions (blindness, reversibility and imperceptibility), a set of linear convex functions which satisfy these requirements are found. Then the optimum of this function set with the least distortion has been selected. The main advantage of this method is that the inserted distortion can be easily controlled by adjusting quantization levels. The low computational complexity is another advantage of this method. Experimental results show that the proposed algorithm achieves higher embedding capacity while its distortion is lower than other invertible watermarking... 

    Fuzzy motion interpolation for mesh-based motion estimation

    , Article 2007 IEEE Symposium on Computational Intelligence in Image and Signal Processing, CIISP 2007, Honolulu, HI, 1 April 2007 through 5 April 2007 ; 2007 , Pages 101-106 ; 1424407079 (ISBN); 9781424407071 (ISBN) Eslami, A ; Sadati, N ; Jahed, M ; Sharif University of Technology
    Mesh-based motion estimation is an important tool for video coding especially with low bit rate. In this paper, a new method for interpolating pixel motion from adjacent mesh nodes with the ability of omitting independent nodes is proposed. By exploiting fuzzy rules to determine the association of pixel and neighboring nodes, the proposed interpolation can detach pixels from some nodes. Consequently, it can deal with those critical patches on objects boundary which their nodes do not belong to one object. Updating the membership functions of each rule with specified strategy makes the interpolation adaptive with non-stationary conditions of image sequences and decreases sensitivity to...