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Added immutable keyword argument to canonical_form function #39196

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Added immutable keyword argument to canonical_form function #39196

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15 changes: 14 additions & 1 deletion src/sage/graphs/bliss.pyx
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Original file line number Diff line number Diff line change
Expand Up @@ -377,7 +377,7 @@ cdef canonical_form_from_edge_list(int Vnr, list Vout, list Vin, int Lnr=1, list
return new_edges


cpdef canonical_form(G, partition=None, return_graph=False, use_edge_labels=True, certificate=False) noexcept:
cpdef canonical_form(G, partition=None, return_graph=False, use_edge_labels=True, certificate=False, immutable=False) noexcept:
r"""
Return a canonical label for the given (di)graph.

Expand All @@ -404,6 +404,9 @@ cpdef canonical_form(G, partition=None, return_graph=False, use_edge_labels=True
- ``certificate`` -- boolean (default: ``False``); when set to ``True``,
returns the labeling of G into a canonical graph

- ``immutable`` -- boolean (default: ``False``); when set to ``True``,
returns an immutable canonical label of the graph

TESTS::

sage: from sage.graphs.bliss import canonical_form # optional - bliss
Expand Down Expand Up @@ -503,6 +506,13 @@ cpdef canonical_form(G, partition=None, return_graph=False, use_edge_labels=True
Traceback (most recent call last):
...
ValueError: some vertices of the graph are not in the partition

Check that parameter ``immutable`` can be used::

sage: g = Graph({1: [2]})
sage: g_ = canonical_form(g, return_graph=True, immutable=True) # optional - bliss
sage: g_.is_immutable() # optional - bliss
True
"""
# We need this to convert the numbers from <unsigned int> to <long>.
# This assertion should be true simply for memory reasons.
Expand Down Expand Up @@ -589,6 +599,9 @@ cpdef canonical_form(G, partition=None, return_graph=False, use_edge_labels=True
H.add_vertices(range(G.order()))
return (H, relabel) if certificate else H

if immutable:
H = H.copy(immutable=True)

# Warning: this may break badly in Python 3 if the graph is not simple
return (sorted(new_edges), relabel) if certificate else sorted(new_edges)

Expand Down
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