Unexpected output with parallel boundary edges

[basudha-srivastava]

When decoding this matching graph:

from pymatching import Matching
import matplotlib.pyplot as plt

m = Matching()
m.set_boundary_nodes({0, 3, 4})
m.add_edge(0, 1, fault_ids=0, weight=2.6, merge_strategy='independent')
m.add_edge(1, 2, fault_ids=1, weight=2.6, merge_strategy='independent')
m.add_edge(2, 3, fault_ids=2, weight=5.3, merge_strategy='independent')
m.add_edge(2, 4, fault_ids=3, weight=2.6, merge_strategy='independent')
m.add_edge(0, 3, weight=0.0)
m.add_edge(0, 4, weight=0.0)
m.add_edge(4, 3, weight=0.0)

z_error = m.decode([0, 0, 1, 0, 0])

print(z_error)

pymatching outputs [1 1 0 0] but I would have expected [0 0 0 1]. Do you know what the reason could be for this? Thanks!

[oscarhiggott]

Hi Basudha, thanks for flagging this, this issue has now been fixed in PR #86 (which correctly outputs [0 0 0 1] for your example) and the fix will be released in the next version of pymatching.