Quadratic Word Equations with Length Constraints, Counter Systems, and Presburger Arithmetic with Divisibility

Word equations are a crucial element in the theoretical foundation of constraint solving over strings, which have received a lot of attention in recent years. A word equation relates two words over string variables and constants. Its solution amounts to a function mapping variables to constant strings that equate the left and right hand sides of the equation. While the problem of solving word equations is decidable, the decidability of the problem of solving a word equation with a length constraint (i.e., a constraint relating the lengths of words in the word equation) has remained a long-standing open problem. In this paper, we focus on the subclass of quadratic word equations, i.e., in which each variable occurs at most twice. We first show that the length abstractions of solutions to quadratic word equations are in general not Presburger-definable. We then describe a class of counter systems with Presburger transition relations which capture the length abstraction of a quadratic word equation with regular constraints. We provide an encoding of the effect of a simple loop of the counter systems in the theory of existential Presburger Arithmetic with divisibility (PAD). Since PAD is decidable, we get a decision procedure for quadratic words equations with length constraints for which the associated counter system is \emph{flat} (i.e., all nodes belong to at most one cycle). We show a decidability result (in fact, also an NP algorithm with a PAD oracle) for a recently proposed NP-complete fragment of word equations called regular-oriented word equations, together with length constraints. Decidability holds when the constraints are additionally extended with regular constraints with a 1-weak control structure.Comment: 18 page

Connecting Forumulas

Objectives: Students will use the graphing calculator to solve quadratic equations. They will analyze the graph and/or table to factor and solve a quadratic equation. Students will then use this technique to solve word problems

The Hardness of Solving Simple Word Equations

We investigate the class of regular-ordered word equations. In such equations, each variable occurs at most once in each side and the order of the variables occurring in both left and right hand sides is preserved (the variables can be, however, separated by potentially distinct constant factors). Surprisingly, we obtain that solving such simple equations, even when the sides contain exactly the same variables, is NP-hard. By considerations regarding the combinatorial structure of the minimal solutions of the more general quadratic equations we obtain that the satisfiability problem for regular-ordered equations is in NP. The complexity of solving such word equations under regular constraints is also settled. Finally, we show that a related class of simple word equations, that generalises one-variable equations, is in P

Upper Bounds on the Length of Minimal Solutions to Certain Quadratic Word Equations

It is a long standing conjecture that the problem of deciding whether a quadratic word equation has a solution is in NP. It has also been conjectured that the length of a minimal solution to a quadratic equation is at most exponential in the length of the equation, with the latter conjecture implying the former. We show that both conjectures hold for some natural subclasses of quadratic equations, namely the classes of regular-reversed, k-ordered, and variable-sparse quadratic equations. We also discuss a connection of our techniques to the topic of unavoidable patterns, and the possibility of exploiting this connection to produce further similar results

Analisis Kesalahan Siswa Dalam Menyelesaikan Soal Cerita Materi Persamaan Kuadrat Berdasarkan Prosedur Newman

This study aims to determine errors and factors that cause students to make mistakes in solving word problems on quadratic equations based on the Newman procedure. The type of research used is descriptive research. Data collection techniques used were written tests, interviews and documentation. The research subjects were 20 students of class IXA at SMP Kristen Tomohon. The results showed that in solving word problems on the quadratic equation material given by the students they still made mistakes based on the Newman procedure. Factors causing students to make mistakes, namely: misreading the numbers in the problem, confused with the formula that students will use in a hurry to solve the problem so they don't write down the final answer. Based on the results of this study, it is suggested to mathematics teachers to provide story questions to students by applying Newman's procedure so that the answers given are more structured

Hambatan Epistemologi (Epistemological Obstacles) Dalam Persamaan Kuadrat Pada Siswa Madrasah Aliyah

Mathematics is basic knowledge for the students. That is need by student, to continue their education to higher levels. The purpose of learning mathematics did not just limit to the knowledge in the calculations, but more importantly, when individuals understand the math, their thinking become more rational and critical. The goal of learning mathematics is to equip student with problem solving ability. Quadratic equation is one of the school mathematics curriculum. Development of concepts and strategies in the quadratic equation illustrate can be developed mathematical communication ability, mathematical connections, mathematical reasoning and mathematical problem-solving. In fact many students have difficulty in understanding the concept of quadratic equations. This study examined the epistemological obstacles that were reviewed from three aspects. The first is aspects of the tendency to rely on deceptive intuitive experiences, this aspect of the tendency to generalise and trend aspects is the obstacles caused by natural language. The method used in this study was a case study, and take the subject of research of 36 students answer in Islamic Senior High School (MAN 2) Bandung who sat in class XII IPA. The study found that 90.56% due to their the tendency to rely on deceptive intuitive experiences, 95.56% due to the tendency to generalise, and 96.67% due to the obstacles caused by natural language. Key Word: Learning Obstacles, Epistemological Obstacles, Quadratic Equations, problem-solving abilit