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2017 Software Open Access OPEN
NOSA-ITACA 1.1
Binante V, Girardi M, Padovani C, Pasquinelli G, Pellegrini D, Porcelli M, Robol L
NOSA-ITACA is a code for the nonlinear structural analysis of historical masonry constructions. It the result of the integration of the finite element code NOSA into the open-source SALOME platform.

See at: CNR IRIS Open Access | ISTI Repository Open Access | www.nosaitaca.it Open Access | CNR IRIS Restricted


2017 Conference article Restricted
NOSA-ITACA: a free FE program for historic masonry buildings
Girardi M, Padovani C, Pellegrini D, Robol L
This paper describes the main features of NOSA-ITACA, a finite-element code for the structural analysis of masonry constructions of historical interest and reports on its application to the structural analysis of some historic buildings in Italy.

See at: CNR IRIS Restricted | CNR IRIS Restricted | www.eccomas.org Restricted


2017 Contribution to book Restricted
Solving large scale quasiseparable Lyapunov equations
Massei S, Palitta D, Robol L
We consider the problem of efficiently solving Lyapunov and Sylvester equations of medium and large scale, in the case where all the coefficients are quasiseparable, i.e., they have off-diagonal blocks of low-rank. This comprises the case with banded coefficients and right-hand side, recently studied in [6, 9]. We show that, under suitable assumptions, this structure is guaranteed to be numer- ically present in the solution, and we provide explicit estimates of the numerical rank of the off-diagonal blocks. Moreover, we describe an efficient method for approximating the solution, which relies on the technology of hierarchical matrices. A theoretical characterization of the quasiseparable structure in the solution is pre- sented, and numerically experiments confirm the applicability and efficiency of our ap- proach. We provide a MATLAB toolbox that allows easy replication of the experiments and a ready-to-use interface for our solver.

See at: cmmse.usal.es Restricted | CNR IRIS Restricted | CNR IRIS Restricted


2017 Journal article Open Access OPEN
Fast Hessenberg reduction of some rank structured matrices
Gemignani L, Robol L
We develop two fast algorithms for Hessenberg reduction of a structured matrix $A = D + UV^H$, where $D$ is a real or unitary n x n diagonal matrix and $U, V in mathbb{C}^{n times k}$. The proposed algorithm for the real case exploits a two-stage approach by first reducing the matrix to a generalized Hessenberg form and then completing the reduction by annihilation of the unwanted subdiagonals. It is shown that the novel method requires O(n^2 k) arithmetic operations and is significantly faster than other reduction algorithms for rank structured matrices. The method is then extended to the unitary plus low rank case by using a block analogue of the CMV form of unitary matrices. It is shown that a block Lanczos-type procedure for the block tridiagonalization of Re(D) induces a structured reduction on A in a block staircase CMV-type shape. Then, we present a numerically stable method for performing this reduction using unitary transformations and show how to generalize the subdiagonal elimination to this shape, while still being able to provide a condensed representation for the reduced matrix. In this way the complexity still remains linear in k and, moreover, the resulting algorithm can be adapted to deal efficiently with block companion matrices.Source: SIAM JOURNAL ON MATRIX ANALYSIS AND APPLICATIONS, vol. 38 (issue 2), pp. 574-598
DOI: 10.1137/16m1107851
DOI: 10.48550/arxiv.1612.04196
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See at: arXiv.org e-Print Archive Open Access | SIAM Journal on Matrix Analysis and Applications Open Access | epubs.siam.org Open Access | CNR IRIS Open Access | ISTI Repository Open Access | SIAM Journal on Matrix Analysis and Applications Restricted | doi.org Restricted | CNR IRIS Restricted | CNR IRIS Restricted