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Assignment on Extensive-Form Games

We consider the following problem: your agent is placed on an island with a map. The goal of the agent is to reach the destination square on the island while collecting as many gold treasures as possible while stepping at each square at most once. There are bandits on the island that want to ambush the agent and steal the collected gold. The bandits may be placed at specific squares (termed “dangerous places”, marked as “E” in the map); there can be at most one bandit at one dangerous place. Your agent only knows the overall number of bandits, however, he does not know the exact places where they are waiting. The bandits want to harm your agent as much as possible by deciding at which dangerous places they are going to wait. When your agent visits a place with a bandit, an attack occurs. The attack is successful with some probability p (the agent will lose all the gold and the game ends). Otherwise, the attack was unsuccessful and your agent can continue. Your agent can react to the information gained during the course of the game – e.g., in the case of an unsuccessful attack, the agent can exploit this information (there is one less bandit in the remaining dangerous places).

The bandits primarily decide their position at the beginning of the game. Moreover, the bandits can use sensors. If your agent enters an unoccupied dangerous place, an alarm is triggered and 1 bandit can relocate to another empty dangerous place. However, this can happen at most once. The following holds:

  • the alarm is triggered only when the agent visits an unoccupied dangerous place for the first time
  • there is at most 1 alarm during the game,
  • if the first dangerous place the agent visits is occupied with a bandit, there will be no alarm triggered (now, nor any later in the game)
  • bandit knows which dangerous place caused the alarm (i.e., the bandits know the actual position of the agent in the time of the alarm)
  • a bandit can be relocated (does not have to be) and it cannot be relocated to the dangerous place where there is another bandit or the agent

Your ultimate goal is to:

  1. formalize this problem as a two-player zero-sum extensive-form game, and
  2. implement the sequence-form linear program for this game and solve it using an external LP solver

In order to successfully accomplish this goal, a report that is required before the full implementation. The report consists of two parts:

  1. A source code that manually constructs two linear programs (one for each player) specifically for one example listed below (marked as “Example for Report”) and solves these linear programs with an external solver. This is for you to test whether you understand the problems when constructing the sequence form before implementing a more general approach.
  2. A text report that contains the extensive-form game tree corresponding to the “Example for Report” that describes your choices for actions/sequences and describes the reasoning behind LPs for the report. It is OK to write/draw it down by hand and submit a picture as long as it is readable and understandable.

Deadline:

Reports: 28.11.2018 4:00 CET 5.12.2018 4:00 CET [5 pts.]

Final : 12.12.2018 4:00 CET 16.12.2018 4:00 CET [12 pts.]

IMPORTANT

  • You can use CPLEX (links for the download are below) or Gurobi for solving LPs (you can download that with an academic license yourself).
  • If you want to use other programming languages than Java or Python, consult with me first (submitting your solution in an unsupported language can result in a significant grading penalization).
  • If you choose to use Python, use Gurobi as your LP solver. The integration is much smoother compared to CPLEX and API is easier to work with.
  • The assignment is graded manually since the most important part is to correctly model the problem as an extensive-form game, which means to correctly identify states, actions, sequences, and information sets.

Input

The assignment is to implement the program for solving described games. The program takes one argument (the input file) with the following format:

number: number of rows of the maze (M)
number: number of columns of the maze (N)
M rows, N symbols representing squares of the maze
number: the overall number of the bandits
float number: the probability of a successful attack

Squares of the maze are defined as follows:

# - obstacle
- - empty square
S - start of your agent
D - destination of your agent
G - gold treasure
E - dangerous place

Constants for Utility Calculation:
Your agent receives 10 points for reaching the destination and he receives 1 additional point for each collected gold treasure. If a bandit successfully attacks the agent, your agent receives 0 points no matter how many gold treasures he has been carrying before the attack. If your agent follows a path that does not end in the destination square (e.g., if it leads to a dead end), your agent receives 0 points.

Input Example:

7
9
#########
#E----EG#
#-##-##E#
#S##-##-#
#-##-##-#
#E-----D#
#########
2
0.5

Output

The output of your program consists of several parts. First, on the standard output write out all the following information.

(1) a list of the sequences for each of the players:

AGENT:
S1:[first_sequence]
S2:[second_sequence]
...
ATTACKER:
Q1:[first_sequence]
Q2:[second_sequence]
...

(2) calculated extended utility function g for each combination of sequences (you can exclude the zero ones):

AGENT\ATTACKER |  Q1      |    Q2   | .... |
--------------------------------------------
S1             | g(S1,Q1) | g(S1,Q2)| ...  |
S2             | g(S2,Q1) | g(S2,Q2)| ...  |
...
--------------------------------------------

(3) calculated realization plans of the sequences in Nash equilibrium (list only sequences that are in the support of NE (i.e., they are played with a strictly positive probability)):

SOLUTION_AGENT:
S1:[realization_plan_of_first_sequence]
S2:[realization_plan_of_second_sequence]
...
SOLUTION_ATTACKER:
Q1:[realization_plan_of_first_sequence]
Q2:[realization_plan_of_second_sequence]
...

(4) calculated value of the game:

SOLUTION_VALUE:[value_of_the_game]

(5) export the linear program into the file [your_login_name].lp

Conventions & FAQ

  • Your agent moves in the maze in 4 directions (up, down, left, right).
  • Use the name Main.java for the main java class (or main.py) and place all your classes in one package (or directory) named by your login-name.
  • As soon as the agent reaches the destination square, the game ends.

Examples and Results

The value of the game must be exactly the same (modulo double arithmetic imprecision). If the difference is larger (e.g., >0.001), your solution is still incorrect!

7
9
#########
#G-----E#
#-#####-#
#S--E--D#
#-#####-#
#G-----E#
#########
2
0.5
the value of the game: 7.096774193548387

7
9
#########
#G-E---E#
#-#####-#
#S-E--ED#
#-#####-#
#G-E---E#
#########
2
0.6
the value of the game: 3.4064516129032265

7
9
#########
#E----EG#
#-##-##E#
#S##-##-#
#-##-##-#
#E-----D#
#########
2
0.5
the value of the game: 5.5

EXAMPLE FOR THE REPORT

5
7
#######
#E---E#
#S#-#D#
#E--EG#
#######
1
0.7
the value of the game: 5.054761904761906

CPLEX-Java Integration

As a linear-program solver you can use IBM ILOG CPLEX. It can be downloaded using the following links:

If you do not know the password, ask us (or your colleagues).

Using ILOG CPlex

Integrating CPLEX with java project: It is necessary to add cplex.jar to your project from …/CPLEX_STUDIO/cplex/lib/cplex.jar, javadocs can be found in …/CPLEX_STUDIO/doc/html/refjavacplex/html.

Running the program: java -Djava.library.path=[path_to_ILOG]/CPLEX_STUDIO/cplex/bin/[architektura:x86-64_sles10_4.1] …

LP initialization: IloCplex cplex = new IloCplex();

Variable initialization: IloNumVar V = cplex.numVar([lower_bound],[upper_bound], [typ:IloNumVarType], [name]);

Creating a generic mathematical expression:

IloNumExpr zero = cplex.constant(0);
IloNumExpr sum = cplex.sum(cplex.prod(2,zero),V); // (2*0 + V)

Creating a generic inequality in the LP: cplex.addGe(sum,V);

Creating dual variables in the LP: IloRange constraint = cplex.addGe(cplex.diff(sum,V),0);

Adding theobjective to the LP: cplex.addMaximize(V);

Exporting the LP to a text file: cplex.exportModel(“file_name.lp”);

Solving the LP: cplex.solve();

Reading the state of the algorithm (whether the solution is 'optimal' or some error has occurred): cplex.getStatus();

Reading the value of the variable: cplex.getValue(V);

Reading the value of dual variables: cplex.getDuals(constraint);

courses/be4m36mas/assignment2-game.txt · Last modified: 2018/11/25 23:45 by bosanbra