Piecewise-Linear Vineyard

Given a simplicial complex K, and a sequence of values on each one of its vertices, one may construct a homotopy of PL functions on the complex that interpolates linearly between the values. For any given time in the homotopy, we get a function from the simplicial complex to the real line, and we can compute its persistence diagram. Stacking all such diagrams together we get a persistence vineyard [CEM06]. An example that computes such a vineyard is in examples/pl-functions/pl-vineyard.cpp.

Once compiled, it takes three files as the input:

pl-vineyard complex values output-prefix

complex lists the simplices of the simplicial complex K, one per-line:

0 1
0 2

values lists the vertex values of the consequtive “frames” of the homotopy. Each line is a sequence of as many numbers as there are vertices in the complex. It describes a single frame. pl-vineayrd constructs the homotopy over the interval [0,k-1], where k is the number of frames. As an example of values input:

3.3   6    2
1.2   3    10
7.5   2.1  0

This input means: f_0(0) = 3.3, f_1(0) = 1.2, f_2(0) = 7.5. Similarly, f_0(1) = 6, f_1(1) = 3, f_2(1) = 2.1; f_0(2) = 2, f_1(2) = 10, f_2(2) = 0.

The vineyard is saved to the files prefixed with output-prefix, followed by the dimension and extension, e.g. myfunction1.vin or myfunction1.edg, depending on the format. The two formats are vines and edges. The former saves one vine per line, listed as a stream of triplets BIRTH DEATH TIME:

4 5 0 3.4 5.6 0.4 3 6 1 ...

The edge format represents the vine as a sequence of edges, each given as a start and end point. So the above vine would appear as:

4 5 0
3.4 5.6 0.4
3.4 5.6 0.4
3 6 1

pl-vineyard takes additional options:

-s, --skip-infinite

Do not output infinite vines.

-v, --save-vines

Output vines, instead of the default edge format.

-e, --explicit-events

Go through the events one by one (useful for the debugging).