{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T21:11:19Z","timestamp":1772745079091,"version":"3.50.1"},"reference-count":0,"publisher":"The Electronic Journal of Combinatorics","issue":"2","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Electron. J. Combin."],"abstract":"<jats:p>Freedman, Lov\u00e1sz 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.<\/jats:p>","DOI":"10.37236\/80","type":"journal-article","created":{"date-parts":[[2020,1,10]],"date-time":"2020-01-10T23:21:59Z","timestamp":1578698519000},"source":"Crossref","is-referenced-by-count":2,"title":["Semidefinite Functions on Categories"],"prefix":"10.37236","volume":"16","author":[{"given":"L\u00e1szl\u00f3","family":"Lov\u00e1sz","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alexander","family":"Schrijver","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"23455","published-online":{"date-parts":[[2009,5,31]]},"container-title":["The Electronic Journal of Combinatorics"],"original-title":[],"link":[{"URL":"https:\/\/www.combinatorics.org\/ojs\/index.php\/eljc\/article\/download\/v16i2r14\/pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/www.combinatorics.org\/ojs\/index.php\/eljc\/article\/download\/v16i2r14\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2020,1,17]],"date-time":"2020-01-17T21:53:11Z","timestamp":1579297991000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.combinatorics.org\/ojs\/index.php\/eljc\/article\/view\/v16i2r14"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2009,5,31]]},"references-count":0,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2009,2,11]]}},"URL":"https:\/\/doi.org\/10.37236\/80","relation":{},"ISSN":["1077-8926"],"issn-type":[{"value":"1077-8926","type":"electronic"}],"subject":[],"published":{"date-parts":[[2009,5,31]]},"article-number":"R14"}}