Hi,
I think I have found a serious bug on Graph.modular_decomposition. Clearly, a
graph is prime if and only if its complement is so. Nevertheless:
sage: P = Graph('Dl_')
sage: P.is_prime()
True
sage: P.complement().is_prime()
False
This behaviour seems to derive from Graph.modular_decomposition. Look:
sage: P.modular_decomposition()
('Prime', [2, 0, 4, 1, 3])
sage: P.complement().modular_decomposition()
('Prime', [('Serie', [3, 1]), 4, 0, 2])
This is not the only example where you can observe this behavior. To generate
easily many examples try, for instance:
sage: for g in graphs(7):
....: if g.is_prime() and not g.complement().is_prime():
....: g.graph6_string()
....:
'Fl_K?'
'FlGK?'
'FlSK?'
'FnsK?'
'Fl[K?'
'FheL?'
'FlUL?'
'F|UL?'
'Fl]L?'
'FlsKG'
'FlUKG'
'FluKG'
'FnV[G'
'FlT[G'
'F|tkG'
'Fl]KG'
'Fl[KW'
'Fn|KG'
'Fn|kG'
'F|LLG'
'FnnLG'
'Flg[?'
'F|g[?'
'Fli[?'
'Flg{?'
'Fn{[?'
'Fn}[?'
'FzN{?'
'F~H[?'
Best regards,
Paulo
--
You received this message because you are subscribed to the Google Groups
"sage-support" group.
To post to this group, send email to sage-support@googlegroups.com.
To unsubscribe from this group, send email to
sage-support+unsubscr...@googlegroups.com.
Visit this group at http://groups.google.com/group/sage-support?hl=en.
