Semidefinite functions on categories
The electronic journal of combinatorics, The Björner Festschrift volume, Tome 16 (2009) no. 2
Freedman, Lovász and Schrijver characterized graph parameters that can be represented as the (weighted) number of homomorphisms into a fixed graph. Several extensions of this result have been proved. We use the framework of categories to prove a general theorem of this kind. Similarly as previous resuts, the characterization uses certain infinite matrices, called connection matrices, which are required to be positive semidefinite.
@article{10_37236_80,
author = {L\'aszl\'o Lov\'asz and Alexander Schrijver},
title = {Semidefinite functions on categories},
journal = {The electronic journal of combinatorics},
year = {2009},
volume = {16},
number = {2},
doi = {10.37236/80},
zbl = {1226.05163},
url = {http://geodesic.mathdoc.fr/articles/10.37236/80/}
}
László Lovász; Alexander Schrijver. Semidefinite functions on categories. The electronic journal of combinatorics, The Björner Festschrift volume, Tome 16 (2009) no. 2. doi: 10.37236/80
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