Suboptimal Travelling Salesman Problem (TSP) solver

In pure Python.

This project provides a pure Python code for searching sub-optimal solutions to the TSP. Additionally, demonstration scripts for visualization of results are provided.

The library does not requires any libraries, but demo scripts require:

• Numpy
• PIL (Python imaging library)
• Matplotlib

Modules provided:

• tsp_solver.greedy : Basic greedy TSP solver in Python
• tsp_solver.greedy_numpy : Version that uses Numpy matrices, which reduces memory use, but performance is several percents lower
• tsp_solver.demo : Code for the demo applicaiton

Scripts provided

• demo_tsp : Generates random TSP, solves it and visualises the result. Optionally, result can be saved to the numpy-format file.
• tsp_numpy2svg : Generates neat SVG image from the numpy file, generated by the demo_tsp.

Both applications support a viriety of command-line keys, run them with --help option to see additional info.

Installation

Standard distutils-based installer is provided. Run the following code to install the library:

 # python setup.py install

Note that in Linux, this will bypass the package management system. Consider using dedicated tools, such as checkinstall.

Alternatively, you may simply copy the tsp_solver/greedy.py to your project.

Usage

The library provides a greedy solver for the symmetric TSP.

Basic usage is the following:

from tsp_solver.greedy import solve_tsp

#Prepare the square symmetric distance matrix for 3 nodes:
#  Distance from 0 to 1 is 1.0
#                1 to 2 is 3.0
#                0 to 2 is 2.0
D = [[ 0, 1.0, 2.0],
     [ 1.0, 0, 3.0],
     [ 2.0, 3.0, 0]]

path = solve_tsp( D )

# will print [1,0,2], path with total length of 3.0 units
print path

Distance matrix must be symmetric.

Algorithm

The library implements simple "greedy" algorithm:

1. Initially, each vertex belongs to its own path. Each path has length 1.
2. Find 2 nearest disconnected paths and connect them.
3. Repeat, until there are at leats 2 paths.

This algorightm has polynomial complexity.

Optimization

Greedy algorithm sometimes produces highly non-optimal solutions. To solve this, optimization is provided. It tries to rearrange points in the paths to improve the solution. One optimization pass has O(n^4) complexity. Note that even unlimited number of optimization paths does not guarantees to find the optimal solution.

Performance

This library neither implements a state-of-the-art algorithm, nor it is tuned for a high performance.

It however can find a decent suboptimal solution for the TSP with 4000 points in several minutes. The biggest practical limitation is memory: O(n^2) memory is used.

Demo

To see a demonstration, run

$ make demo

without installation. The demo requires Numpy and Matplotlib python libraries to be installed.