{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,16]],"date-time":"2026-05-16T16:29:11Z","timestamp":1778948951012,"version":"3.51.4"},"reference-count":32,"publisher":"American Mathematical Society (AMS)","issue":"264","license":[{"start":{"date-parts":[[2009,2,25]],"date-time":"2009-02-25T00:00:00Z","timestamp":1235520000000},"content-version":"am","delay-in-days":366,"URL":"https:\/\/www.ams.org\/publications\/copyright-and-permissions"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Math. Comp."],"abstract":"<p>\n                    In this article we design and analyze multilevel preconditioners for linear systems arising from regularized inverse problems. Using a scale-independent distance function that measures spectral equivalence of operators, it is shown that these preconditioners approximate the inverse of the operator to optimal order with respect to the spatial discretization parameter\n                    <inline-formula content-type=\"math\/mathml\">\n                      <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"h\">\n                        <mml:semantics>\n                          <mml:mi>h<\/mml:mi>\n                          <mml:annotation encoding=\"application\/x-tex\">h<\/mml:annotation>\n                        <\/mml:semantics>\n                      <\/mml:math>\n                    <\/inline-formula>\n                    . As a consequence, the number of preconditioned conjugate gradient iterations needed for solving the system will\n                    <bold>decrease<\/bold>\n                    when increasing the number of levels, with the possibility of performing only one fine-level residual computation if\n                    <inline-formula content-type=\"math\/mathml\">\n                      <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"h\">\n                        <mml:semantics>\n                          <mml:mi>h<\/mml:mi>\n                          <mml:annotation encoding=\"application\/x-tex\">h<\/mml:annotation>\n                        <\/mml:semantics>\n                      <\/mml:math>\n                    <\/inline-formula>\n                    is small enough. The results are based on the previously known two-level preconditioners of Rieder (1997) (see also Hanke and Vogel (1999)), and on applying Newton-like methods to the operator equation\n                    <inline-formula content-type=\"math\/mathml\">\n                      <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"upper X Superscript negative 1 Baseline minus upper A equals 0\">\n                        <mml:semantics>\n                          <mml:mrow>\n                            <mml:msup>\n                              <mml:mi>X<\/mml:mi>\n                              <mml:mrow class=\"MJX-TeXAtom-ORD\">\n                                <mml:mo>\n                                  \u2212\n                                  \n                                <\/mml:mo>\n                                <mml:mn>1<\/mml:mn>\n                              <\/mml:mrow>\n                            <\/mml:msup>\n                            <mml:mo>\n                              \u2212\n                              \n                            <\/mml:mo>\n                            <mml:mi>A<\/mml:mi>\n                            <mml:mo>=<\/mml:mo>\n                            <mml:mn>0<\/mml:mn>\n                          <\/mml:mrow>\n                          <mml:annotation encoding=\"application\/x-tex\">X^{-1} - A = 0<\/mml:annotation>\n                        <\/mml:semantics>\n                      <\/mml:math>\n                    <\/inline-formula>\n                    . We require that the associated forward problem has certain smoothing properties; however, only natural stability and approximation properties are assumed for the discrete operators. The algorithm is applied to a reverse-time parabolic equation, that is, the problem of finding the initial value leading to a given final state. We also present some results on constructing restriction operators with preassigned approximating properties that are of independent interest.\n                  <\/p>","DOI":"10.1090\/s0025-5718-08-02100-5","type":"journal-article","created":{"date-parts":[[2008,7,25]],"date-time":"2008-07-25T12:55:42Z","timestamp":1216990542000},"page":"2001-2038","source":"Crossref","is-referenced-by-count":11,"title":["Optimal order multilevel preconditioners for regularized ill-posed problems"],"prefix":"10.1090","volume":"77","author":[{"given":"Andrei","family":"Dr\u0103g\u0103nescu","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Todd","family":"Dupont","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"14","published-online":{"date-parts":[[2008,2,25]]},"reference":[{"key":"1","unstructured":"Volkan Ak\u00e7elik, George Biros, Andrei Dr\u0103g\u0103nescu, Omar Ghattas, Judith C. Hill, and Bart G. van Bloemen Waanders, Dynamic data driven inversion for terascale simulations: Real-time identification of airborne contaminants, Proceedings of SC2005 (Seattle, WA), IEEE\/ACM, November 2005."},{"issue":"153","key":"2","doi-asserted-by":"publisher","first-page":"35","DOI":"10.2307\/2007724","article-title":"An optimal order process for solving finite element equations","volume":"36","author":"Bank, Randolph E.","year":"1981","journal-title":"Math. 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Comp.","ISSN":"https:\/\/id.crossref.org\/issn\/0025-5718","issn-type":"print"},{"key":"7","series-title":"Texts in Applied Mathematics","isbn-type":"print","doi-asserted-by":"publisher","DOI":"10.1007\/978-1-4757-3658-8","volume-title":"The mathematical theory of finite element methods","volume":"15","author":"Brenner, Susanne C.","year":"2002","ISBN":"https:\/\/id.crossref.org\/isbn\/0387954511","edition":"2"},{"key":"8","isbn-type":"print","doi-asserted-by":"publisher","DOI":"10.1137\/1.9780898719505","volume-title":"A multigrid tutorial","author":"Briggs, William L.","year":"2000","ISBN":"https:\/\/id.crossref.org\/isbn\/0898714621","edition":"2"},{"key":"9","volume-title":"Calcul diff\\'{e}rentiel","author":"Cartan, Henri","year":"1967"},{"key":"10","unstructured":"E. G. D\u2019Jakanov, On an iterative method for the solution of a system of finite difference equations, Dokl. Akad. Nauk. SSSR 138 (1961), 522\u2013525."},{"key":"11","unstructured":"Andrei Dr\u0103g\u0103nescu, A fast multigrid method for inverting linear parabolic problems, Tech. Report TR-2004-01, University of Chicago, Department of Computer Science, 2004, presented at the Eighth Copper Mountain Conference on Iterative Methods."},{"key":"12","unstructured":"\\bysame, Two investigations in numerical analysis: Monotonicity preserving finite element methods, and multigrid methods for inverse parabolic problems, Ph.D. thesis, University of Chicago, August 2004."},{"key":"13","unstructured":"Andrei Dr\u0103g\u0103nescu and Todd F. Dupont, A multigrid algorithm for backwards reaction-diffusion equations, in preparation."},{"key":"14","doi-asserted-by":"publisher","first-page":"753","DOI":"10.1137\/0705058","article-title":"A factorization procedure for the solution of elliptic difference equations","volume":"5","author":"Dupont, Todd","year":"1968","journal-title":"SIAM J. Numer. 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