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Review Test1. Robotics & Future Technology. Future of Intelligent Systems. Ray Kurzweil futurist A Long Bet Robot Soccer BBC News - What happened to the Robotic Age ? Robotic Dance?. CHAPTER 5. REVIEW of some important concepts to remember….
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Future of Intelligent Systems • Ray Kurzweilfuturist • A Long Bet • Robot Soccer • BBC News - What happened to the Robotic Age? • Robotic Dance?
CHAPTER 5 REVIEW of some important concepts to remember…
Constraint Satisfaction A constraint satisfaction problem (CSP) is a problem composed of variables and constraints. The objective is to assign values to variable in such a way that all of the constraints are satisfied. A CSP can be more formally viewed as a triple <D,X,C> where: • D represents a set of n domains • X represents a set of n variables, each variable xi takes it value from Di • C represents a set of constraints.
Two types of CSPs • Finite domain CSPs • Queens, Domains, Boolean • Infinite Domain CSPs • If Job1 takes 5 days, then Job3 will start • Job1 +5 < Job3
thrashing Wasteful” backtracking is known as
Variable & Value Ordering • Variable order selection seldom results in the most efficient search • One efficient strategy • Minimum Remaining Value (MRV) which chooses the value with the fewest legal values • A.K.A “Most Constrained Value” • A.K.A “Fail-First” Heuristic because it is the most likely to cause failure first
Propagating through constraints • Forward Checking is a better use of constraints • When every variable X is assigned, the forward checking process looks at each unassigned variable Y AND Deletes from Y’s domain any value that is inconsistent with the value chosen for X. • Think of Forward Checking as a way to incrementally compute the info needed for MRV to do its job
Arc Consistency • nother backtrack-based algorithm that is even more efficient is called the maintaining arc consistency (MAC) algorithm. • Arc Consistency provides fast method of constraint propagation stronger than forward checking. • Arc Consistency can be provided as preprocessing step (just as forward checking can be used to preprocess).
MAC Algorithm p146 • Rather than just revising each domain corresponding with the value of each instantiated variable MAC makes the network arc-consistent with respect to the instantiated variables (all arcs must be consistent). • MAC is applied repeatedly until no more inconsistencies remain. • Node Consistency • 1- consistency means that each individual variable by itself is consistent (node consistency) • 2- consistency is arc consistency • 3- consistency means that any pair of adjacent variables can always be extended to a third neighboring variable (i.e. path consistency or AC-3) • AC-3 uses a queue to keep track of nodes that need to be checked for inconsistency
Intelligent backtracking: looking backward • Chronological backtracking: a policy for when a branch of the search fails by backing up to the preceding variable and try a different value for it • Chronological uses the more recent decision point to revisit
Things that cause a failure • The conflict set • Backjumping backtracks to the most recent variable in the conflict set