Papers by Alireza hasanpour bagheri
arXiv (Cornell University), Mar 27, 2018
Given a simple polygon P of n vertices in the Plane. We study the problem of computing the visibi... more Given a simple polygon P of n vertices in the Plane. We study the problem of computing the visibility area from a given viewpoint q inside P where only sub-linear variables are allowed for working space. Without any memory-constrained, this problem was previously solved in O(n)-time and O(n)-variables space. In a newer research, the visibility area of a point be computed in O(n)time, using O(√ n) variables for working space. In this paper, we present an optimal-time algorithm, using O(c/ log n) variables space for computing visibility area, where c < n is the number of critical vertices. We keep the algorithm in the linear-time and reduce space as much as possible.
arXiv (Cornell University), Aug 4, 2017
Given a graph G with n vertices and a set S of n points in the plane, a point-set embedding of G ... more Given a graph G with n vertices and a set S of n points in the plane, a point-set embedding of G on S is a planar drawing such that each vertex of G is mapped to a distinct point of S. A straight-line point-set embedding is a point-set embedding with no edge bends or curves. The point-set embeddability problem is NP-complete, even when G is 2-connected and 2-outerplanar. It has been solved polynomially only for a few classes of planar graphs. Suppose that S is the set of vertices of a simple polygon. A straight-line polygon embedding of a graph is a straight-line point-set embedding of the graph onto the vertices of the polygon with no crossing between edges of graph and the edges of polygon. In this paper, we present O(n)-time algorithms for polygon embedding of path and cycle graphs in simple convex polygon and same time algorithms for polygon embedding of path and cycle graphs in a large type of simple polygons where n is the number of vertices of the polygon.
arXiv (Cornell University), Aug 4, 2017
Given an orthogonal polygon P with n vertices, the goal of the watchman route problem is finding ... more Given an orthogonal polygon P with n vertices, the goal of the watchman route problem is finding a path S of the minimum length in P such that every point of the polygon P is visible from at least one of the point of S. In the other words, in the watchman route problem we must compute a shortest watchman route inside a simple polygon of n vertices such that all the points interior to the polygon and on its boundary are visible to at least one point on the route. If route and polygon be orthogonal, it is called orthogonal watchman route problem. One of the targets of this problem is finding the orthogonal path with the minimum number of bends as possible. We present a linear-time algorithm for the orthogonal watchman route problem, in which the given polygon is monotone. Our algorithm can be used also for the problem on simple orthogonal polygons P for which the dual graph induced by the vertical decomposition of P is a path, which is called path polygon.
Innovaciencia Facultad de Ciencias Exactas Físicas y Naturales, 2019
The separation of color points is one of the important issues in computational geometry, which is... more The separation of color points is one of the important issues in computational geometry, which is used in various parts of science; it can be used in facility locating, image processing and clustering. Among these, one of the most widely used computational geometry in the real-world is the problem of covering and separating points with rectangles. In this paper, we intend to consider the problemof separating the two-color points sets, using three rectangles. In fact, our goal is to separate desired blue points from undesired red points by three rectangles, in such a way that these three rectangles contain the most desire points. For this purpose, we provide a metaheuristic algorithm based on the simulated annealing method that could separates blue points from input points, , in time order O (n) with the help of three rectangles. The algorithm is executed with C# and also it has been compared and evaluated with the optimum algorithm results. The results show that our recommended algo...
International Journal of Computer Applications, 2014
Quality and execution time are two important factors for evaluation of edge detection algorithms.... more Quality and execution time are two important factors for evaluation of edge detection algorithms. In these algorithms, there is a trade-off between quality and execution time. Some algorithms only concentrate on quality and some of them are fast and low quality. Efficient methods try to achieve high quality in a low time. This research concentrates on improvement of gradient based edge detection that is fast method and appropriate for real-time processing. The proposed algorithm reduces execution time by removing many pixels from computations. It calculates gradient and angle class of remaining pixels in a very efficient way so that it reinforces quality and locality of edges. The results of this algorithm indicated improvement of performance in comparison to Canny and LOG algorithms.
Discrete Applied Mathematics, May 1, 2016
Although, the Hamiltonicity of solid grid graphs are polynomial-time decidable, the complexity of... more Although, the Hamiltonicity of solid grid graphs are polynomial-time decidable, the complexity of the longest cycle problem in these graphs is still open. In this paper, by presenting a linear-time constant-factor approximation algorithm, we show that the longest cycle problem in solid grid graphs is in APX. More precisely, our algorithm finds a cycle of length at least 2n 3 + 1 in 2-connected n-node solid grid graphs.
Journal of Mathematics
A many-to-many matching (MM) between two sets matches each element of one set to at least one ele... more A many-to-many matching (MM) between two sets matches each element of one set to at least one element of the other set. A general case of the MM is the many-to-many matching with demands and capacities (MMDC) satisfying given lower and upper bounds on the number of elements matched to each element. In this article, we give a polynomial-time algorithm for finding a minimum-cost MMDC between two sets using the well-known Hungarian algorithm.
Scientia Iranica
Separation of desired objects from undesired ones is one of the most important problems in comput... more Separation of desired objects from undesired ones is one of the most important problems in computational geometry. It is tended to cover the desired objects by one or a couple of geometric shapes in a way that all of the desired objects are included by the covering shapes, while the undesired objects are excluded. We study separation of polylines by minimal triangles with a given fixed angle and present () O NlogNtime algorithm, where N is the number of all the desired and undesired polylines. By a minimal triangle, we mean a triangle in which all of its edges are tangential to the convex hull of the desired polylines. The motivation for studying this separation problem stems from that we need to separate bichromatic objects that are modeled by polylines not points in real life scenarios.
The Influence of Pyrogenic Nanosilicas with Different Surface Areas and Aggregation States on Cement Hydration
In this study, the pozzolanic activity of pyrogenic nanosilicas with different specific surface a... more In this study, the pozzolanic activity of pyrogenic nanosilicas with different specific surface areas (90m 2 /g, 200m 2 /g and 300m 2 /g) and aggregation states in lime and cement pastes and their effects on cement hydration have been investigated and compared to the influences of silica fume. The results show very rapid pozzolanic activity for the pyrogenic nanosilicas compared to silica fume and the rate increases with increasing specific surface area of nanosilicas. The large differences in the initial aggregate sizes of nanosilicas appear not to influence their pozzolanic activity. Nanosilicas accelerate cement hydration at early ages, however; at later ages, progress in cement hydration is reduced.
ArXiv, 2019
FAST problem is finding minimum feedback arc set problem in tournaments. In this paper we present... more FAST problem is finding minimum feedback arc set problem in tournaments. In this paper we present some algorithms that are similar to sorting algorithms for FAST problem and we analyze them. We present Pseudo_InsertionSort algorithm for FAST problem and we show that average number of all backward edges in output of that is equal to ((n^2-5n+8)/4)-2^(1-n). We introduce Pseudo_MergeSort algorithm and we find the probability of being backward for an edge. Finally we introduce other algorithms for this problem.
In the geometric graph embedding problem, a graph with n vertices and a set of n points in the pl... more In the geometric graph embedding problem, a graph with n vertices and a set of n points in the plane are given, and the aim of embedding is to find a mapping between vertices of the graph to these points in such a way that minimizes the length of the embedded graph on the point set. Since the travelling salesman problem is a special case of the graph embedding problem, therefore, the problem is an NPhard problem. In this paper, we consider a particular case where the given graph is a binary tree. We present four heuristic approaches, then we compare the time complexity, and the resulted embedding length of these algorithms.
The use of the Roller Compacted Concrete (RCC) in the core of the body of gravity dams can consid... more The use of the Roller Compacted Concrete (RCC) in the core of the body of gravity dams can considerably speed up the procedure of the construction. Since there is no post-cooling treatment for RCC dams, it is necessary to analyze the temperature profile of the concrete body for desired plan of the construction. A diffusive equation is coupled to the concrete heat generation equation in order to solve the temperature field. The discrete form of the equations is derived using Galerkin method by application of piece wise linear approximate function. The solution domain is divided into hybrid structured/unstructured triangular fiiite elements, considering gradual movement of the top boundary of the concreting. Application of the software in simulation of temperature profile in a typical RCC dam section is also demonstrated.
Advances in Computer Science : an International Journal, 2015
The Freeze-Tag Problem (FTP) arises in the study of swarm robotics. The FTP is a combinatorial op... more The Freeze-Tag Problem (FTP) arises in the study of swarm robotics. The FTP is a combinatorial optimization problem that starts by locating a set of robots in a Euclidean plane. Here, we are given a swarm of n asleep (frozen or inactive) robots and a single awake (active) robot. In order to activate an inactive robot in FTP, the active robot should either be in the physical proximity to the inactive robot or ``touch`` it. The new activated robot starts moving and can wake up other inactive robots. The goal is to find an optimal activating schedule with the minimum time required for activating all robots. In general, FTP is an NP-Hard problem and in the Euclidean space is an open problem. In this paper, we present a recursive approximation algorithm with a constant approximation factor and a linear running time for the Euclidean Freeze-Tag Problem.
Abstract— The social network embodies real-life social graphs. Detecting communities or clusters ... more Abstract— The social network embodies real-life social graphs. Detecting communities or clusters from these graphs is an ill-posed difficult task. The communities are identified using the adjacent nodes that have shared edges and similar features. One of the principal concerns after community detection is to identify the active nodes in a network who attend several communities. So, finding communities that are overlapped in a social network is an important topic in social network analysis. This paper introduces an algorithm based on the multi-agent particle swarm optimization. The proposed algorithm detects overlapping as well as non-overlapping communities. Following the detection of overlapping communities, this algorithm can identify those nodes leading to overlapping, and ultimately it can determine the affiliation ratio of each node to the given community. The algorithm uses a special type of coding to identify the number of communities without any prior knowledge. In this meth...
Background: A matching between two sets A and B assigns some elements of A to some elements of B.... more Background: A matching between two sets A and B assigns some elements of A to some elements of B. Finding the similarity between two sets of elements by advantage of the matching is widely used in computational biology for example in the contexts of genome-wide and sequencing association studies. Frequently, the capacities of the elements are limited. That is, the number of the elements that can be matched to each element should not exceed a given number. Results: We use bipartite graphs to model relationships between pairs of objects. Given an undirected bipartite graph G = (A [ B;E), the b-matching of G matches each vertex v in A (resp. B) to at least 1 and at most b(v) vertices in B (resp. A), where b(v) denotes the capacity of v. We propose the rst O(n3) time algorithm for nding the maximum weight b-matching of G, where jAj + jBj = O(n). Conclusions: The b-matching has been studied widely for the bipartite graphs with integer weight edges. But our algorithm is the rst algorithm ...
International Journal of Structural and Civil Engineering Research, 2018
When concrete element is exposed to the environment, it undergoes volumetric contraction due to t... more When concrete element is exposed to the environment, it undergoes volumetric contraction due to the drying shrinkage, which when restrained can lead to cracking. Crack width is controlled by the ability of fibers in transmission of stress across the crack opening. In this study the effect of Macro polymeric fibers in controlling drying shrinkage cracking of concrete was investigated and compared with that of steel fibers. The results of restrained ring tests show that at low and medium rate of utilization (0.25 and 0.5%) the effect of macro synthetic fibers are similar to steel fibers. However, at a higher dosage of 1%, steel fibers clearly outperform the polymeric fibers. The shape of macro polymeric fibers (multi-strand or singlestrand) was not found to significantly affect their performance.
Advances in Computer Science an International Journal, Jul 31, 2013
Steiner tree problem leads to solutions in several scientific and business contexts, including co... more Steiner tree problem leads to solutions in several scientific and business contexts, including computer networks routing and electronic integrated circuits. Computing fields of this problem has become an important research topic in computational geometry. Considering the number of points in the Euclidean plane, called terminal points, a minimum spanning tree is obtained which connects these points. A series of other points (Steiner points) are added to the tree, which makes it shorter in length. The resulting tree is called Euclidean Steiner minimal tree. It is considered as an NP-hard problem. Considering a simple polygon P with m vertices and n terminals, in which you are trying to find a Euclidean Steiner tree that is connected to all n terminals existing inside p. In this paper we propose a solution for several terminals in a simple polygonal in presence of obstacles.
Although there are very algorithms for embedding graphs on unbounded grids, only few results on e... more Although there are very algorithms for embedding graphs on unbounded grids, only few results on embedding or drawing graphs on restricted grids has been published. In this work, we consider the problem of embedding paths and cycles on grid graphs. We give the necessary and sufficient conditions for the existence of cycles of given length k and paths of given length k between two given vertices in n-vertex rectangular grid graphs and introduce two algorithms with running times O(k) and O(k 2) for finding respectively such cycles and paths. Also, we extend our results to m×n×o 3D grids. Our method for finding cycle of length k in rectangular grid graphs also introduces a linear-time algorithm for finding cycles of a given length k in hamiltonian solid grid graphs.
Advances in Computer Science an International Journal, Jul 31, 2013
The Steiner tree problem has numerous applications in urban transportation network, design of ele... more The Steiner tree problem has numerous applications in urban transportation network, design of electronic integrated circuits, and computer network routing. This problem aims at finding a minimum Steiner tree in the Euclidean space, the distance between each two edges of which has the least cost. This problem is considered as an NP-hard one. Assuming the simple polygon P with m vertices and n terminals, the purpose of the minimum Steiner tree in the Euclidean space is to connect the n terminals existing in p. In the proposed algorithm, obtaining optimal responses will be sought by turning this problem into the Steiner tree problem on a graph.
Theoretical Computer Science, 2016
We study the Hamiltonian path problem in C−shaped grid graphs, and present the necessary and suff... more We study the Hamiltonian path problem in C−shaped grid graphs, and present the necessary and sufficient conditions for the existence of a Hamiltonian path between two given vertices in these graphs. We also give a linear-time algorithm for finding a Hamiltonian path between two given vertices of a C−shaped grid graph, if it exists.
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Papers by Alireza hasanpour bagheri