Problem Decomposition: Goal Trees, Rule Based Systems, Rule Based Expert Systems. Planning: STRIPS, Forward and Backward State Space Planning, Goal Stack Planning, Plan Space Planning, A Unified Framework For Planning. Constraint Satisfaction : N-Queens, Constraint Propagation, Scene Labeling, Higher order and Directional Consistencies, Backtracking and Look ahead Strategies.

1. Topic To Be Covered:
Techniques(Heuristic) To Improve Backtracking Efficiency
Jagdamba Education Society's
SND College of Engineering & Research Centre
Department of Computer Engineering
SUBJECT: Artificial Intelligence & Robotics
Lecture No-12(UNIT-02)
Prof.Dhakane Vikas N

2. Techniques To Improve Backtracking Efficiency
I. Least Constraining Value
 Given a variable, choose the least constraining value: the one that
rules out the fewest values in the remaining variables.
 It prefer the value that will give more flexibility to its neighbor for
coloring.
 It select such a value which will reduce constraints on its neighbor.

3. Techniques To Improve Backtracking Efficiency
II. Most Constraining Variable
 In this technique we choose the variable with most constraints on
remaining variable( i. e. Here we need to choose region or variable
surrounded by maximum number of regions or variable.)
 Once we assign color to this part of map is as good as we have
decided the color of all the surrounded parts.

4. Techniques To Improve Backtracking Efficiency
III. Most Constrained Variable
 It chooses the variable with fewest legal values.
 Here we need to choose region or variable surrounded by minimum
number of regions or variable
 By assigning this variable first ,we can get a fair idea of other
variable assignment.
 This technique is also called as Minimum remaining value(MRV)
heuristic or forced first heuristic.

5. Techniques To Improve Backtracking Efficiency
IV. Forward Checking
 It keeps track of remaining legal values for unassigned variable.
 Terminate search when any variable has no legal value.
 As shown in figure below as we go on assigning color to different
regions, we noticed that SA is not left with any valid color to
assign.
 Hence assignment will terminate & the process backtrack to
previous state.
 This technique doesn’t provide early detection of failure.

6. Techniques To Improve Backtracking Efficiency
V. Constraint Propagation
 As Forward checking doesn’t provide early detection of failure.
 In CP strategy , as we assign color to one of the parts of map ,the
other part are evaluated for the valid assignment. Hence we can
detect failure early.

7. Techniques To Improve Backtracking Efficiency
V. Constraint Propagation
 As shown in example below, as the region Q is getting assigned
Green color , both NT and SA are left with blue color; but they both
cant have same color as they are adjacent regions.
 Hence the wrong assignment of green to Q region is detected a step
early.

8. Example of CSp : Map Coloring Problem