1 / 11

CSPs

CSPs. Tamara Berg CS 590-133 Artificial Intelligence. Many slides throughout the course adapted from Svetlana Lazebnik , Dan Klein, Stuart Russell, Andrew Moore, Percy Liang, Luke Zettlemoyer. Constraint Satisfaction Problems (Chapter 6). What is search for?.

chaeli
Download Presentation

CSPs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CSPs Tamara Berg CS 590-133 Artificial Intelligence Many slides throughout the course adapted from Svetlana Lazebnik, Dan Klein, Stuart Russell, Andrew Moore, Percy Liang, Luke Zettlemoyer

  2. Constraint Satisfaction Problems(Chapter 6)

  3. What is search for? • Assumptions: single agent, deterministic, fully observable, discrete environment • Search for planning • The path to the goal is the important thing • Paths have various costs, depths • Search for assignment • Assign values to variables while respecting certain constraints • The goal (complete, consistent assignment) is the important thing

  4. Constraint satisfaction problems (CSPs) • Definition: • Xi is a set of variables {X1,… Xn} • Di is a set of domains {D1 ,...Dn}one for each variable • C is a set of constraints that specify allowable combinations of values • Solution is a complete, consistent assignment • How does this compare to the “generic” tree search formulation? • A more structured representation for states, expressed in a formal representation language • Allows useful general-purpose algorithms with more power than standard search algorithms • by eliminating large portions of search space (identifying var/val combinations that violate constraints).

  5. Example: Map Coloring • Variables:WA, NT, Q, NSW, V, SA, T • Domains: {red, green, blue} • Constraints: adjacent regions must have different colorse.g., WA ≠ NT, or (WA, NT) in {(red, green), (red, blue), (green, red), (green, blue), (blue, red), (blue, green)}

  6. Example: Map Coloring • Solutions are complete and consistent assignments, e.g., WA = red, NT = green, Q = red, NSW = green, V = red, SA = blue, T = green

  7. Example: n-queens problem • Put n queens on an n × n board with no two queens in the same row, column, or diagonal

  8. Example: N-Queens • Variables:Xij • Domains: {0, 1} • Constraints: i,j Xij = N (Xij,Xik)  {(0, 0), (0, 1), (1, 0)} (Xij,Xkj)  {(0, 0), (0, 1), (1, 0)} (Xij,Xi+k, j+k)  {(0, 0), (0, 1), (1, 0)} (Xij,Xi+k, j–k)  {(0, 0), (0, 1), (1, 0)} Xij

  9. N-Queens: Alternative formulation • Variables:Qi • Domains: {1, … , N} • Constraints: i, j non-threatening (Qi,Qj) Q1 Q2 Q3 Q4

  10. Example: Cryptarithmetic • Variables: T, W, O, F, U, R X1, X2 • Domains: {0, 1, 2, …, 9} • Constraints: O + O = R + 10 * X1 W + W + X1 = U + 10 * X2 T + T + X2 = O + 10 * F Alldiff(T, W, O, F, U, R) T ≠ 0, F ≠ 0 X2 X1

  11. Example: Sudoku • Variables:Xij • Domains: {1, 2, …, 9} • Constraints: Alldiff(Xij in the same unit) Xij

More Related