Dataset of 4-regular multigraphs for the second Hamiltonian decomposition problem

Each file contains 100 regular multigraphs constructed as unions of Hamiltonian cycles of different nature:
*.txt – unions of random permutations generated by the Fisher-Yates shuffle algorithm;
*pyr.txt – unions of pyramidal tours with only one peak;
*_4peaks.txt – unions of Hamiltonian cycles with exactly four peaks.
A vertex is called a peak in a cycle if its successor and predecessor have lower numbers.
Hamiltonian cycles are encoded as vertex permutations.
The resulting union multigraphs can be considered both undirected and directed.