`unmesh`

Converts a list of mesh edges to a graph adjacency matrix and node coordinates.

Syntax

[A, xy] = unmesh(E)

Returns the adjacency matrix A and node coordinates xy for the edge list E.

Description

Segments that share an end point are connected through the same node: two end points with identical coordinates become one node. The pair A, xy is exactly what gplot needs, so a drawing given as loose line segments can be turned into a graph and analyzed with sparse matrix tools.

Input arguments

E: m-by-4 matrix; each row [x1 y1 x2 y2] is one edge, given by the coordinates of its two end points.

Output arguments

A: Symmetric n-by-n adjacency matrix, with A(i,j) = 1 when nodes i and j share an edge.
xy: n-by-2 matrix with the coordinates of the distinct end points, numbered in order of first appearance.

Example

A triangle from three segments

E = [0 0 1 0; 1 0 0 1; 0 1 0 0];
[A, xy] = unmesh(E);
full(A)
xy

Output

ans = 3×3

     2    -1    -1
    -1     2    -1
    -1    -1     2
xy = 3×2

     0     0
     0     1
     1     0

unmesh