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Proginoskes science forum Guru
Joined: 29 Apr 2005
Posts: 2593

Posted: Mon Feb 27, 2006 11:09 pm Post subject:
Re: LP  Shortest path with customer satisfaction



Richard Dobis wrote:
Quote:  Hi all,
I have been working with the following problem. Example: Travel agency wants
to take people from city A to city B. Of course it want do it in such a way
that minimize total transportation costs. BUT it also looks for a customer
satisfaction. It want to choose the way that gives to customer at least
predefined level of satisfaction.
Model of the problem:
Graph with directed arcs. Cycles are there. It is not a tree. Each arc has
two numbers assigned  c_a: cost of traversing arcs a  p_a: pleasure that
recieve customer by traversing arc a. All numbers c_a and p_a are positive.
Let P by minimal allowed level of pleasure that is acceptable by cusomers.
The LP formulation of the above problem is:
Min Sum_a c_a arc_s
S.t.:
A arc = b  flow conservation constraints
sum_a p_a arc_a >= P
arc_a is binary {0,1}
Simple computing this by LP solver don't deliver a path. Sometimes it
deliver shortest path in the unconstrained sense (like withou pleasure
constraint) and several cycles that are not connected to the shortest path.

c_a is 0 along any edge of any of these cycles, right?
You could get rid of the cycles by replacing c_a = 0 with c_a = (a
small positive number, depending on the data). This shouldn't affect
the minimum path much, and it will eliminate the cycles.
 Christopher Heckman 

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Richard Dobis science forum beginner
Joined: 26 Feb 2006
Posts: 9

Posted: Mon Feb 27, 2006 7:21 am Post subject:
LP  Shortest path with customer satisfaction



Hi all,
I have been working with the following problem. Example: Travel agency wants
to take people from city A to city B. Of course it want do it in such a way
that minimize total transportation costs. BUT it also looks for a customer
satisfaction. It want to choose the way that gives to customer at least
predefined level of satisfaction.
Model of the problem:
Graph with directed arcs. Cycles are there. It is not a tree. Each arc has
two numbers assigned  c_a: cost of traversing arcs a  p_a: pleasure that
recieve customer by traversing arc a. All numbers c_a and p_a are positive.
Let P by minimal allowed level of pleasure that is acceptable by cusomers.
The LP formulation of the above problem is:
Min Sum_a c_a arc_s
S.t.:
A arc = b  flow conservation constraints
sum_a p_a arc_a >= P
arc_a is binary {0,1}
Simple computing this by LP solver don't deliver a path. Sometimes it
deliver shortest path in the unconstrained sense (like withou pleasure
constraint) and several cycles that are not connected to the shortest path.
I need hint for solving this problem. How to transform above formulation to
the resource constrained shortest path problem? Any arcicles?
In the similar case where p_a is not pleasure but resource, time or risk the
model is as follows:
Min Sum_a c_a arc_s
S.t.:
A arc = b  flow conservation constraints
sum_a t_a arc_a <= T
arc_a is binary {0,1}
where t_a>=0 is time that consumes traversing arc a.
Interpretation is as follows: Travel agency look for cheapest path from city
A to city B that lasts at most T.
In this case simple LP solver deliver solution that is acceptable.
Thank you for any hint  advice, article, idea ....
richard 

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