Earth-Moon problem Algorithms

Algorithms for work on the earth-moon problem. Current two different algorithms (sharing helper functions):

• biplanarTester: backtracking algorithm to determine if a given graph is biplanar.
• candidateBuilder: brute-force algorithm that searches for thickness-2 graphs of a chosen chromatic number.

Both inherit functions form the module helperFunctions.

Directory structure

.
├── cpp/
│   ├── helperFunctions.h
│   ├── helperFunctions.cpp
│   ├── biplanarTester.h
│   ├── biplanarTester.cpp
│   ├── candidateBuilder.h
│   ├── candidateBuilder.cpp
│   ├── biplanarSAT.h
│   ├── biplanarSAT.cpp
│   └── main.cpp
├── data/
├── python/
│   ├── utils/
│   │   ├── graphUtils.py
│   │   ├── visUtils.py
│   │   └── outputUtils.py
│   ├── vis/
│   │   ├── drawGraph.py
│   │   ├── partitionsColored.py
│   │   └── planePartitions.py
│   ├── ilp/
│   │   └── biplanarILP.py
│   ├── sat/
│   │   ├── biplanarBlowupSAT.py
│   │   └── biplanarSAT.py
│   └── requirements.txt
└── Makefile

cpp

The cpp code has the actual algorithm implementations.

• helperFunctions.cpp includes functions to construct graphs, test planarity, and some other helpful things.
• biplanarTester.cpp has the implementation of the backtracking recursive code to determine if a given graph is biplanar by building different edge partitions.
• candidateBuilder.cpp has the implementation of the code to build candidate graphs of chromatic number at least 9 and/or 10 with a certain number of vertices.
• *.h are simply the header file, they contain function prototypes and datastructures.
• main.cpp is simply where the code is run from. Here you choose what graph to test biplanarity for, or what parameters to use when searching for biplanarity graphs of high chromatic number.

Every function is commented, so if something is unclear consider looking through the codebase.

python

To install the requirements run pip install -r python/requirements.txt

The python/utils directory contains helper function.

The python/vis directory contain scode to draw the graphs.

• drawGraph.py draws the graph from the file passed as an argument (default: data/test.txt).
• partitionsColored.py draws the graph from the file passed as an argument (default: ~/data/partitions.txt) with the two partitions colored red and blue.
• planePartitions.py draws the partitions of the graph from the file passed as an argument (default: in data/partitions.txt) as plane graphs (if possible). Example graph files can be found under data

The python/ilp and python/sat directories contain the code for the ILP and SAT solvers to find biplanar partitions of graphs (respectively). They (attempt to) find biplanar partitions of the graph from the file passed as argument (default: data/test.txt).

data

The data directory is where we store different graphs and partitions. The cpp code writes to the directory, and the python code reads from it.

The format to describe a graph/two partitions is clear from reading the .txt files in the directory.

Running the project

To run the code first run

make clean 
make 
make run

Biplanar test

The graph you want to check biplanarity of can be described in cpp/main.cpp, check helperFunctions.h to see the different graphs that can be used (path, cycle and complete) and operations that can be applied on them (removeVertex, strongProduct).

You can also manually define the graph.

Once the edge-set is defined, simply call isBiplanar(edges, 0, g1, g2); (also from main.cpp), where g1,g2 are empty graphs on n vertices. To avoid symmetric case, you can consider adding the first edge to g1 and instead calling isBiplanar(edges, 1, g1, g2);.

If a partition is found, it will be ouput data/partitions.txt.

Candidate builder

Simply call computeCandidateGraphs(int numVertLow, int numVertHigh, int numAttempts); from main.cpp where numVertLow, numVertHigh, numAttempts are respectively the lower number of vertices to find a graph for, the highest number of vertices, and the number of attempts per each number of vertices.

If finds a biplanar graph of chromatic number \geq 9 or 10, the graph and the two partitions are saved at:

• data/candidates{x}/graph_{i}_{n}.txt where {x} is 9 or 10 (chromatic number), {i} current attempt, and {n} number of vertices of the graph.

Graph visualizing

Drawing the graph (if biplanar) can be done via make drawPart (to get the graph with one partition in red, the other in blue) and make plane to get the plane drawings of both partitions. By default it will plot the partitions from data/partitions.txt, but you can choose a different one by passing the path as an argument (e.g. make draw data/p3_k4_partitioned.txt). For exampel, to plot a candidate graph, you'd have to call make drawPart data/candidates10/graph_10_50.txt (or with make plane).

To simply draw an arbitrary graph (not partitioned) use make draw and give the (relative) file path as input when asked (e.g. c5_44443.txt), or pass it directly (e.g. make draw c5_44443.txt).

ILP and SAT

Simply run make ilp and make sat respectively, passing as argument the file describing the graph. If a partition is found, it is saved to data/SAT_partition.txt and data/ILP_partition.txt respectively.

TODO

A sat implementation of the biplanar tester has been written on cpp, although it might be a bit buggy. A sat implementation for blow-ups has been written on python.