I. Hill climbing algorithm II. Steepest hill climbing algorithm

Topic To Be Covered:
I. Hill climbing algorithm
II. Steepest hill climbing algorithm
Jagdamba Education Society's
SND College of Engineering & Research Centre
Department of Computer Engineering
SUBJECT: Artificial Intelligence & Robotics
Lecture No-14(Unit-01)
Prof.Dhakane Vikas N

Hill climbing algorithm IN AI
 Hill climbing algorithm is a local search algorithm which continuously
moves in the direction of increasing elevation/value to find the peak of the
mountain or best solution to the problem.
 It terminates when it reaches a peak value where no neighbor has a higher
value.
 It is also called greedy local search as it only looks to its good immediate
neighbor state and not beyond that.
 A node of hill climbing algorithm has two components which are state and
value.
 Hill Climbing is mostly used when a good heuristic is available.

 Hill Climbing is mostly used when a good
heuristic is available.
Following are some main features of Hill
Climbing Algorithm:
 Generate and Test variant: Hill Climbing is
the variant of Generate and Test method. The
Generate and Test method produce feedback
which helps to decide which direction to
move in the search space.
 Greedy approach: Hill-climbing algorithm
search moves in the direction which
optimizes the cost.
 No backtracking: It does not backtrack the
search space, as it does not remember the
previous states.

Types of Hill Climbing Algorithm
I. Simple hill Climbing
 Simple hill climbing is the simplest
way to implement a hill climbing
algorithm.
 It only evaluates the neighbor node
state at a time and selects the first one
which optimizes current cost and set it
as a current state.
 It only checks it's one successor state,
and if it finds better than the current
state, then move else be in the same
state.
This algorithm has the following features:
 Less time consuming
 Less optimal solution and the solution
is not guaranteed

I. Algorithm for Simple hill Climbing
Step 1: Evaluate the initial state, if it is goal state
then return success and Stop.
Step 2: Loop Until a solution is found or there is
no new operator left to apply.
Step 3: Select and apply an operator to the
current state.

I. Algorithm for Simple hill Climbing
Step 4: Check new state:
 If it is goal state, then return success and
quit.
 Else if it is better than the current state then
assign new state as a current state
 Else if not better than the current state, then
return to step 2
Step 5: Exit.

II. Steepest-Ascent hill climbing
 The steepest-Ascent algorithm is a variation
of simple hill climbing algorithm.
 This algorithm examines all the neighboring
nodes of the current state and selects one
neighbor node which is closest to the goal
state.
 This algorithm consumes more time as it
searches for multiple neighbors

II. Steepest-Ascent hill climbing Algorithm
Step 1 : Evaluate the initial state. If it is goal
state then exit else make the current state as
initial state
Step 2 : Repeat these steps until a solution is
found or current state does not change
i. Let GS be a state such that any successor of
the current state will be better than it;

II. Steepest-Ascent hill climbing Algorithm
ii. for each operator that applies to the current
state
a. apply the new operator and create a new state
b. evaluate the new state
c. if this state is goal state then quit else
compare with GS
d. if this state is better than GS, set this state as
GS
e. if GS is better than current state set current
state to GS
Step 3 :Exit.

Problems in Hill Climbing Algorithm:
1. Local Maximum: A local maximum is a peak state in the landscape
which is better than each of its neighboring states, but there is
another state also present which is higher than the local maximum.
Solution: Backtracking technique can be a solution of the local
maximum in state space landscape. Create a list of the promising path
so that the algorithm can backtrack the search space and explore other
paths as well.

2. Plateau: A plateau is the flat area of the search space in which all the
neighbor states of the current state contains the same value, because
of this algorithm does not find any best direction to move. A hill-
climbing search might be lost in the plateau area.
Solution: The solution for the plateau is to take big steps or very little
steps while searching, to solve the problem. Randomly select a state
which is far away from the current state so it is possible that the
algorithm could find non-plateau region.

3. Ridges: A ridge is a special form of the local maximum. It has an
area which is higher than its surrounding areas, but itself has a slope,
and cannot be reached in a single move.
Solution: With the use of bidirectional search, or by moving in
different directions, we can improve this problem.

I. Hill climbing algorithm II. Steepest hill climbing algorithm

I. Hill climbing algorithm II. Steepest hill climbing algorithm

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