@prefix prodottidellaricerca: . @prefix istituto: . @prefix prodotto: . istituto:CDS044 prodottidellaricerca:prodotto prodotto:ID156695 . @prefix pubblicazioni: . @prefix unitaDiPersonaleInterno: . unitaDiPersonaleInterno:MATRICOLA6076 pubblicazioni:autoreCNRDi prodotto:ID156695 . @prefix rdf: . @prefix retescientifica: . prodotto:ID156695 rdf:type retescientifica:ProdottoDellaRicerca , prodotto:TIPO1715 . @prefix rdfs: . prodotto:ID156695 rdfs:label "Regularizing preconditioners based on fit techniques in the image reconstruction problem (Rapporti tecnici, manuali, carte geologiche e tematiche e prodotti multimediali)"@en . @prefix xsd: . prodotto:ID156695 pubblicazioni:anno "2002-01-01T00:00:00+01:00"^^xsd:gYear . @prefix skos: . prodotto:ID156695 skos:altLabel "
Favati P., Lotti G., Menchi O. (2002)
Regularizing preconditioners based on fit techniques in the image reconstruction problem
"^^rdf:HTML ; pubblicazioni:autori "Favati P., Lotti G., Menchi O."^^xsd:string ; pubblicazioni:note "Technical report 2002-TR-18"^^xsd:string ; pubblicazioni:descrizioneSinteticaDelProdotto "Regularizing preconditioners for the approximate solution by gradient-type methods of image restoration problems with two-level band Toeplitz structure, are examined. For problems having separable and positive definite matrices, the fit preconditioner, introduced in [6], has been shown to be effective in conjunction with CG. The cost of this preconditioner is of O(n^2) operations per iteration, where n^2 is the pixels number of the image, whereas the cost of the circulant preconditioners commonly used for this type of problems is of O(n^2 log n) operations per iteration. In this paper the extension of the fit preconditioner to more general cases is proposed: namely the nonseparable positive definite case and the symmetric indefinite case are treated. The major difficulty encountered in this extension concerns the factorization phase, where, unlike the separable case, a further approximation is required. Various approximate factorizations are proposed. The preconditioners thus obtained have still a cost of O(n^2) operations per iteration. A large numerical experimentation compares these preconditioners with the circulant Chan preconditioner, showing often better performances at a lower cost."^^xsd:string ; pubblicazioni:supporto "Memorie interne"^^xsd:string ; pubblicazioni:titolo "Regularizing preconditioners based on fit techniques in the image reconstruction problem"^^xsd:string ; prodottidellaricerca:prodottoDi istituto:CDS044 ; pubblicazioni:autoreCNR unitaDiPersonaleInterno:MATRICOLA6076 . @prefix parolechiave: . prodotto:ID156695 parolechiave:insiemeDiParoleChiave . parolechiave:insiemeDiParoleChiaveDi prodotto:ID156695 .