Marching Squares

Overview

Marching squares for wall-bounded and periodic boundaries.

Motivation

On one hand just for fun (99%). On the other hand (1%) I wanted to extend contour in Matplotlib for periodic domains.

Dependency

• C compiler
• GNU make (not essential but recommended)
• Gnuplot (not essential but recommended)

Quick start

Sample dataset is attached (in data directory) for stand-alone execution:

$ make
$ ./a.out

Result is written to clusters.dat, which is an ASCII file containing coordinates of each polygonal chain. They can be visualised by Gnuplot, e.g.,

$ plot 'clusters.dat' u 1:2 w lp

API

The main function of this library is make_clusters, which is declared as

int make_clusters(
    const bool periods[2],
    const double lengths[2],
    const size_t sizes[2],
    const double threshold,
    const double * restrict xs,
    const double * restrict ys,
    const double * restrict values,
    size_t * restrict nclusters,
    cluster_t *** restrict clusters
);

Parameters:

• periods

  Boundary condition of two directions, periodic (true) or not (false)

• lengths

  Physical sizes

• sizes

  Number of grid points

• threshold

  Threshold to draw contour lines

• xs

  x coordinate (length of this vector should be sizes[0])

• ys

  y coordinate (length of this vector should be sizes[1])

• values

  Two-dimensional scalar field

• nclusters

  Result, number of clusters

• clusters

  Result, all polygonal chains

Documentation

Minor but non-trivial things are documented here.