The Experts below are selected from a list of 48831 Experts worldwide ranked by ideXlab platform
Tero Harju - One of the best experts on this subject based on the ideXlab platform.
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On the n-permutation Post Correspondence Problem
Theoretical Computer Science, 2015Co-Authors: Mari Ernvall, Vesa Halava, Tero HarjuAbstract:We give new and simpler proof for the undecidability of the n-permutation Post Correspondence Problem that was originally proved by K. Ruohonen 10. Our proof uses a recent result on deterministic semi-Thue systems according to which it is undecidable for a given deterministic semi-Thue system T and a word u whether or not there exists a nonempty cyclic derivation u ? T + u in T.
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post Correspondence Problem and small dimensional matrices
Developments in Language Theory, 2009Co-Authors: Tero HarjuAbstract:This is a survey on some undecidable Problems on integer matrices. The proofs of these results employ special instances, called Claus instances, of the Post Correspondence Problem. The presentation is based on the article Halava et al. "Undecidability bounds for integer matrices using Claus instances" (Internat. J. Foundations of Comput. Sci. 18, 2007, 931---948).
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Developments in Language Theory - Post Correspondence Problem and Small Dimensional Matrices
Developments in Language Theory, 2009Co-Authors: Tero HarjuAbstract:This is a survey on some undecidable Problems on integer matrices. The proofs of these results employ special instances, called Claus instances, of the Post Correspondence Problem. The presentation is based on the article Halava et al. "Undecidability bounds for integer matrices using Claus instances" (Internat. J. Foundations of Comput. Sci. 18, 2007, 931---948).
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Post Correspondence Problem for short words
Information Processing Letters, 2008Co-Authors: Vesa Halava, Tero Harju, Mika Hirvensalo, Juhani KarhumäkiAbstract:We prove that the generalized Post Correspondence Problem is undecidable for instances where the lengths of the image words are at most 2 and the number of pairs of words is at most 30. The proof uses undecidability of the word Problem of the Tzeitin semigroup. We also transform our constructions in order to achieve a proof for the undecidability of the (not generalized) Post Correspondence Problem with image words of length at most 2.
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Undecidability of infinite post Correspondence Problem for instances of Size 9
RAIRO - Theoretical Informatics and Applications, 2006Co-Authors: Vesa Halava, Tero HarjuAbstract:In the infinite Post Correspondence Problem an instance (h,g) consists of two morphisms h and g , and the Problem is to determine whether or not there exists an infinite word ω such that h(ω) = g(ω) . This Problem was shown to be undecidable by Ruohonen (1985) in general. Recently Blondel and Canterini (Theory Comput. Syst. 36 (2003) 231–245) showed that this Problem is undecidable for domain alphabets of size 105. Here we give a proof that the infinite Post Correspondence Problem is undecidable for instances where the morphisms have domains of 9 letters. The proof uses a recent result of Matiyasevich and Senizergues and a modification of a result of Claus.
Joaquim Salvi - One of the best experts on this subject based on the ideXlab platform.
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RECENT PROGRESS IN CODED STRUCTURED LIGHT AS A TECHNIQUE TO SOLVE THE Correspondence Problem: A SURVEY
Pattern Recognition, 1998Co-Authors: J Batlle, El Mustapha Mouaddib, Joaquim SalviAbstract:We present a survey of the most significant techniques, used in the last few years, concerning the coded structured light methods employed to get 3D information. In fact, depth perception is one of the most important subjects in computer vision. Stereovision is an attractive and widely used method, but, it is rather limited to make 3D surface maps, due to the Correspondence Problem. The Correspondence Problem can be improved using a method based on structured light concept, projecting a given pattern on the measuring surfaces. However, some relations between the projected pattern and the reflected one must be solved. This relationship can be directly found codifying the projected light, so that, each imaged region of the projected pattern carries the needed information to solve the Correspondence Problem.
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recent progress in structured light in order to solve the Correspondence Problem in stereovision
International Conference on Robotics and Automation, 1997Co-Authors: El Mustapha Mouaddib, J Batlle, Joaquim SalviAbstract:We present a summary of the most significant techniques, used in the last few years, concerning the coded structured light methods employed to get 3D information. In fact, depth perception is one of the most important subjects in computer vision. Stereovision is an attractive and widely used method, but, rather limited to make 3D surface maps, due to the Correspondence Problem. The Correspondence Problem can be improved using a method based on a structured light concept, projecting a given pattern on the measuring surfaces, although some relations between the projected pattern and the reflected one must be solved. This relationship can be directly found codifying the projected light, so that, each imaged region of the projected pattern carries the necessary information to solve the Correspondence Problem. We do not need to mention the numerous advantages in accurate obtention of 3D information for many research subjects, such as: robotics, autonomous navigation, shape analysis, and so on.
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ICRA - Recent progress in structured light in order to solve the Correspondence Problem in stereovision
Proceedings of International Conference on Robotics and Automation, 1Co-Authors: El Mustapha Mouaddib, J Batlle, Joaquim SalviAbstract:We present a summary of the most significant techniques, used in the last few years, concerning the coded structured light methods employed to get 3D information. In fact, depth perception is one of the most important subjects in computer vision. Stereovision is an attractive and widely used method, but, rather limited to make 3D surface maps, due to the Correspondence Problem. The Correspondence Problem can be improved using a method based on a structured light concept, projecting a given pattern on the measuring surfaces, although some relations between the projected pattern and the reflected one must be solved. This relationship can be directly found codifying the projected light, so that, each imaged region of the projected pattern carries the necessary information to solve the Correspondence Problem. We do not need to mention the numerous advantages in accurate obtention of 3D information for many research subjects, such as: robotics, autonomous navigation, shape analysis, and so on.
Vesa Halava - One of the best experts on this subject based on the ideXlab platform.
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On the n-permutation Post Correspondence Problem
Theoretical Computer Science, 2015Co-Authors: Mari Ernvall, Vesa Halava, Tero HarjuAbstract:We give new and simpler proof for the undecidability of the n-permutation Post Correspondence Problem that was originally proved by K. Ruohonen 10. Our proof uses a recent result on deterministic semi-Thue systems according to which it is undecidable for a given deterministic semi-Thue system T and a word u whether or not there exists a nonempty cyclic derivation u ? T + u in T.
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WORDS - Deterministic Semi-Thue Systems and Variants of Post Correspondence Problem
Lecture Notes in Computer Science, 2013Co-Authors: Vesa HalavaAbstract:We study recent undecidability result on deterministic semi-Thue systems, and it is applications in the variants of Post Correspondence Problem. Namely, we discuss the ideas of the new proofs for the circular PCP and the n-permutation PCP.
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reduction tree of the binary generalized post Correspondence Problem
International Journal of Foundations of Computer Science, 2011Co-Authors: Vesa Halava, Stěpan HolubAbstract:An instance of the (Generalized) Post Correspondence Problem is during the decision process typically reduced to one or more other instances, called its successors. In this paper we study the reduction tree of GPCP in the binary case. This entails in particular a detailed analysis of the structure of end blocks. We give an upper bound for the number of end blocks, and show that even if an instance has more than one successor, it can nevertheless be reduced to a single instance. This, in particular, implies that binary GPCP can be decided in polynomial time.
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On post Correspondence Problem for letter monotonic languages
Theoretical Computer Science, 2009Co-Authors: Vesa Halava, Jarkko Kari, Yuri MatiyasevichAbstract:We prove that for given morphisms g,h:{a"1,a"2,...,a"n}->B^*, it is decidable whether or not there exists a word w in the regular language a"1^*a"2^*...a"n^* such that g(w)=h(w). In other words, we prove that the Post Correspondence Problem is decidable if the solutions are restricted to be from this special language. This yields a nice example of an undecidable Problem in integral matrices which cannot be directly proved undecidable using the traditional reduction from the Post Correspondence Problem.
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Post Correspondence Problem for short words
Information Processing Letters, 2008Co-Authors: Vesa Halava, Tero Harju, Mika Hirvensalo, Juhani KarhumäkiAbstract:We prove that the generalized Post Correspondence Problem is undecidable for instances where the lengths of the image words are at most 2 and the number of pairs of words is at most 30. The proof uses undecidability of the word Problem of the Tzeitin semigroup. We also transform our constructions in order to achieve a proof for the undecidability of the (not generalized) Post Correspondence Problem with image words of length at most 2.
Roberto Casati - One of the best experts on this subject based on the ideXlab platform.
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The copycat solution to the shadow Correspondence Problem
Perception, 2007Co-Authors: Roberto CasatiAbstract:Cast shadows (henceforth simply ‘shadows') depicted in artworks can fulfil some of their perceptual roles, such as helping the retrieval of 3d structure and of relative positions of objects, without having to be geometrically or physically accurate. The visual system displays a wide tolerance for shadows that are mostly inaccurate, at times making use of the scarce accurate but relevant information that can still be retrieved from them. However, the extent of the tolerable inaccuracy is at present still unexplored. We propose that inaccuracy can be not only totally acceptable but in some cases is even likely to be preferable to accuracy if the main perceptual role of shadows is to help locate in a scene the objects that cast them. We examined a small but effective historical corpus of pictorial endeavours, from which it appears that in some cases painters have used a copycat strategy for drawing the terminator of a shadow, i.e. they have produced a replica of the visible profile of the caster, which in the norm yields an impossible shadow. The copycat strategy is perceptually effective for solving the Correspondence Problem of associating a shadow with its caster; copycatting can be more effective than other solutions, including the depiction of the geometrically correct shadow, and is complementary to coarser solutions to the Correspondence Problem. These phenomena provide insight into the computations effectively used by the brain to deal with space perception. In particular, the brain is not relying on some sort of simplified physical model of the world, for the shadows produced by the copycat effect would correspond to a more complicated physical situation than the one encountered in real life.
El Mustapha Mouaddib - One of the best experts on this subject based on the ideXlab platform.
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RECENT PROGRESS IN CODED STRUCTURED LIGHT AS A TECHNIQUE TO SOLVE THE Correspondence Problem: A SURVEY
Pattern Recognition, 1998Co-Authors: J Batlle, El Mustapha Mouaddib, Joaquim SalviAbstract:We present a survey of the most significant techniques, used in the last few years, concerning the coded structured light methods employed to get 3D information. In fact, depth perception is one of the most important subjects in computer vision. Stereovision is an attractive and widely used method, but, it is rather limited to make 3D surface maps, due to the Correspondence Problem. The Correspondence Problem can be improved using a method based on structured light concept, projecting a given pattern on the measuring surfaces. However, some relations between the projected pattern and the reflected one must be solved. This relationship can be directly found codifying the projected light, so that, each imaged region of the projected pattern carries the needed information to solve the Correspondence Problem.
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recent progress in structured light in order to solve the Correspondence Problem in stereovision
International Conference on Robotics and Automation, 1997Co-Authors: El Mustapha Mouaddib, J Batlle, Joaquim SalviAbstract:We present a summary of the most significant techniques, used in the last few years, concerning the coded structured light methods employed to get 3D information. In fact, depth perception is one of the most important subjects in computer vision. Stereovision is an attractive and widely used method, but, rather limited to make 3D surface maps, due to the Correspondence Problem. The Correspondence Problem can be improved using a method based on a structured light concept, projecting a given pattern on the measuring surfaces, although some relations between the projected pattern and the reflected one must be solved. This relationship can be directly found codifying the projected light, so that, each imaged region of the projected pattern carries the necessary information to solve the Correspondence Problem. We do not need to mention the numerous advantages in accurate obtention of 3D information for many research subjects, such as: robotics, autonomous navigation, shape analysis, and so on.
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ICRA - Recent progress in structured light in order to solve the Correspondence Problem in stereovision
Proceedings of International Conference on Robotics and Automation, 1Co-Authors: El Mustapha Mouaddib, J Batlle, Joaquim SalviAbstract:We present a summary of the most significant techniques, used in the last few years, concerning the coded structured light methods employed to get 3D information. In fact, depth perception is one of the most important subjects in computer vision. Stereovision is an attractive and widely used method, but, rather limited to make 3D surface maps, due to the Correspondence Problem. The Correspondence Problem can be improved using a method based on a structured light concept, projecting a given pattern on the measuring surfaces, although some relations between the projected pattern and the reflected one must be solved. This relationship can be directly found codifying the projected light, so that, each imaged region of the projected pattern carries the necessary information to solve the Correspondence Problem. We do not need to mention the numerous advantages in accurate obtention of 3D information for many research subjects, such as: robotics, autonomous navigation, shape analysis, and so on.
