Recognizing Visibility Graphs of Polygons with Holes and Internal-External Visibility Graphs of Polygons

Visibility graph of a polygon corresponds to its internal diagonals and boundary edges. For each vertex on the boundary of the polygon, we have a vertex in this graph and if two vertices of the polygon see each other there is an edge between their corresponding vertices in the graph. Two vertices of a polygon see each other if and only if their connecting line segment completely lies inside the polygon, and they are externally visible if and only if this line segment completely lies outside the polygon. Recognizing visibility graphs is the problem of deciding whether there is a simple polygon whose visibility graph is isomorphic to a given input graph. This problem is well-known and well-studied, but yet widely open in geometric graphs and computational geometry. Existential Theory of the Reals is the complexity class of problems that can be reduced to the problem of deciding whether there exists a solution to a quantifier-free formula F(X1,X2,...,Xn), involving equalities and inequalities of real polynomials with real variables. The complete problems for this complexity class are called Existential Theory of the Reals Complete. In this paper we show that recognizing visibility graphs of polygons with holes is Existential Theory of the Reals Complete. Moreover, we show that recognizing visibility graphs of simple polygons when we have the internal and external visibility graphs, is also Existential Theory of the Reals Complete.Comment: Sumbitted to COCOON2018 Conferenc

Investigation of the Profitability of the Methods of Selecting for Predicting the Risk of Stock Price Fall in the supply chain of Companies Listed in Tehran Stock Exchange

The aim of this study was to investigate the profitability of variable reduction methods for predicting the risk of the stock price drop of companies listed in Tehran Stock Exchange. To achieve this, the literature review was conducted and 24 primary variables were selected which were most frequently used in the literature and the required data for measuring them was available. The optimum variables were selected or extracted among the primary variables using variable selection methods (the correlation-based method and the relief method) and variable extraction methods (the factor analysis and the principal component analysis). Then, the risk of stock price fall for 101 companies listed in Tehran Stock Exchange was predicted for 2001-2015 using linear regression. In order to evaluate the performanceof the variable reduction methods, the evaluation criteria resulting from prediction using variables selected or extracted by these methods were compared with criteria resulting from prediction using all variables. Findings of the research indicated the profitability of variable reduction methods and significant differences between profitability levels of different methods. The results obtained from the investigation of the performance of different methods of prediction and variable reduction in the industry group indicated the effect of the type of industry on the prediction performance. Furthermore, the results of the prediction of returns during 2001-2015 showed that the performance of prediction was higher in some years and lower in some other years compared to the results of the collective investigation of the supply chain of companies in this period

Studying the effect of voluntary disclosure changes on firm value

The main purpose of the present research is studying the effect of voluntary disclosure changes on firm value in accepted firms at Tehran stock exchange. Using Feltham and Ohlson's model (1995), the present research has discussed the effect of investors’ reaction to net operating assets and abnormal operating earnings for firms changing their voluntary disclosure. Data analysis was carried out in two steps in this research; at first based on changing in the amount of voluntary disclosure member firms of statistical sample were divided to firms with reduction in disclosure and firms with increase in disclosure then research hypotheses were tested. Results from 420 firm-year during 2006-2011 showed that managers of firms whose firm values are undervalued by investors increase voluntary disclosure of information

The US exchange rate behavior: an advanced test on price parity theorem

We researched a significant topic on exchange rate behavior by restating the test procedures in a novel manner and applying an appropriate econometric methodology to re-examine exchange rate behavior of the US economy. The central research question is: Do inflation differences across two economies fully account for exchange rate changes, if controls for non-parity factors are embedded while controlling for interest rate differences? The results affirm, for the first time, that price parity factor holds well while other factors - interest rates and non-parity factors - also affect exchange rates significantly. Our tests also identifies the time to equilibrium to be 0.139 (13.9%) per quarter to adjust to equilibrium value. In our view, these findings extend our knowledge of how the US dollar behavior is consistent with parity and non-parity theorems. Prior tests have been inconclusive on parity factors. The Malaysian Ringgit is heavily dependent on the US dollar exchange rate, and our findings thus have monetary policy implications for the Malaysia's regulators

Parity Theorems Revisited: An Ardl Bound Test With Non-parity Factors

The research question addressed in this paper is, do inflation and interest rate differences across two major economies fully drive the long-run exchange rate changes if controls for non-parity factors are embedded? Exchange rate behaviour research is once again an interesting topic given the availability of powerful econometric approaches to resolve unsolved issues. We re-examine the exchange rate behaviour of the US economy, applying a more appropriate econometric model using 55 years of quarterly data. The model explains 96% of variation in exchange rates, which testifies to the model’s appropriateness. The error correction estimate indicates a time-to-equilibrium of 0.139 per quarter; that is, full adjustment takes seven quarters. Tests indicate evidence of a long-run relationship among the exchange rate, prices, and interest rates. The coefficients on both parity factors (prices and interest rates) are statistically significant with correct theory-suggested signs. These findings constitute strong evidence in support of parity and non-parity theorems while confirming that the US currency behaviour over 1960–2014 is consistent with parity and non-parity theorie

Does It Make a Difference? L2 Vocabulary Learning via Mobile and Conventional Mode

The present study investigated the significance of mobile learning (m-learning) of English vocabulary items through a traditional contrasted with a blended method of content representation. To achieve the goals, sixty semi-illiterate adults were evaluated for their knowledge of the English alphabet and then randomly placed in two groups: traditional (G1) and the blended group (G2). Next, they were presented thirty new English vocabulary items through the two methods. Also, the vocabulary items were taught with and without pictorial annotations. Upon the completion of teaching, the participants took the paper-and-pencil-based English Vocabulary Recognition and Recall (EVRR) test. The test results were subjected to the appropriate statistical analyses. The analysis demonstrated the supremacy of blended group's performance over the traditional group in vocabulary learning. Furthermore, the obtained results confirmed that pictorial annotations enhanced the learning of L2 vocabulary compared with non-annotated items. The results can provide some practical and theoretical implications for both teachers and learners

Identifying components of international social cataloging sites to present criteria for native model

Abstract The purpose of this article is to provide criteria for native model of social cataloging sites based on the world\u27s most visited, popular social cataloging site\u27s components. Social cataloging sites are a kind of web-based social media that allows users to interact. This is an applied research and the research method is library and descriptive scrolling. First, by reviewing the scientific literature and resources, a list consists of 14 criteria which included 73 extracted components, then finalized in Delphi and evaluated was used. The community studied also includes three social cataloging sites, which have the most visitors on the Alexa ranking. The results of this study showed that the total score for the fourteen criteria considered in this study was173/31points. The average of observance of criteria in all social cataloging sites(58.10%)is above the average and is in a favorable situation. Goodreads ranked first among the sites listed in the study list with 46 points(63.01%).after that LT is ranked second by the score of45points(61.64%) and anobi reached third rank with36.25points(49.65). All of the components examined in this study are important and the search facilities with an average of 9.70have the highest importance and error messages with an average of9.24are ranked second