{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,24]],"date-time":"2026-03-24T05:18:38Z","timestamp":1774329518314,"version":"3.50.1"},"reference-count":23,"publisher":"American Mathematical Society (AMS)","issue":"280","license":[{"start":{"date-parts":[[2013,3,2]],"date-time":"2013-03-02T00:00:00Z","timestamp":1362182400000},"content-version":"am","delay-in-days":365,"URL":"https:\/\/www.ams.org\/publications\/copyright-and-permissions"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Math. Comp."],"abstract":"<p>Discontinuous Galerkin (DG) methods exhibit \u201chidden accuracy\u201d that makes superconvergence of this method an increasing popular topic to address. Previous investigations have focused on the superconvergent properties of ordinary differential equations and linear hyperbolic equations. Additionally, superconvergence of order <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"k plus three halves\">\n  <mml:semantics>\n    <mml:mrow>\n      <mml:mi>k<\/mml:mi>\n      <mml:mo>+<\/mml:mo>\n      <mml:mfrac>\n        <mml:mn>3<\/mml:mn>\n        <mml:mn>2<\/mml:mn>\n      <\/mml:mfrac>\n    <\/mml:mrow>\n    <mml:annotation encoding=\"application\/x-tex\">k+\\frac {3}{2}<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> for the convection-diffusion equation that focuses on a special projection using the upwind flux was presented by Cheng and Shu. In this paper we demonstrate that it is possible to extend the smoothness-increasing accuracy-conserving (SIAC) filter for use on the multi-dimensional linear convection-diffusion equation in order to obtain 2<inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"k\">\n  <mml:semantics>\n    <mml:mi>k<\/mml:mi>\n    <mml:annotation encoding=\"application\/x-tex\">k<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula>+<inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"m\">\n  <mml:semantics>\n    <mml:mi>m<\/mml:mi>\n    <mml:annotation encoding=\"application\/x-tex\">m<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> order of accuracy, where <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"m\">\n  <mml:semantics>\n    <mml:mi>m<\/mml:mi>\n    <mml:annotation encoding=\"application\/x-tex\">m<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> depends upon the flux and takes on the values <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"0 comma one half comma\">\n  <mml:semantics>\n    <mml:mrow>\n      <mml:mn>0<\/mml:mn>\n      <mml:mo>,<\/mml:mo>\n      <mml:mspace width=\"thinmathspace\"\/>\n      <mml:mfrac>\n        <mml:mn>1<\/mml:mn>\n        <mml:mn>2<\/mml:mn>\n      <\/mml:mfrac>\n      <mml:mo>,<\/mml:mo>\n    <\/mml:mrow>\n    <mml:annotation encoding=\"application\/x-tex\">0,\\, \\frac {1}{2},<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> or <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"1 period\">\n  <mml:semantics>\n    <mml:mn>1.<\/mml:mn>\n    <mml:annotation encoding=\"application\/x-tex\">1.<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> The technique that we use to extract this hidden accuracy was initially introduced by Cockburn, Luskin, Shu, and S\u00fcli for linear hyperbolic equations and extended by Ryan et al. as a smoothness-increasing accuracy-conserving filter. We solve this convection-diffusion equation using the local discontinuous Galerkin (LDG) method and show theoretically that it is possible to obtain <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"script upper O left-parenthesis h Superscript 2 k plus m Baseline right-parenthesis\">\n  <mml:semantics>\n    <mml:mrow>\n      <mml:mrow class=\"MJX-TeXAtom-ORD\">\n        <mml:mi class=\"MJX-tex-caligraphic\" mathvariant=\"script\">O<\/mml:mi>\n      <\/mml:mrow>\n      <mml:mo stretchy=\"false\">(<\/mml:mo>\n      <mml:msup>\n        <mml:mi>h<\/mml:mi>\n        <mml:mrow class=\"MJX-TeXAtom-ORD\">\n          <mml:mn>2<\/mml:mn>\n          <mml:mi>k<\/mml:mi>\n          <mml:mo>+<\/mml:mo>\n          <mml:mi>m<\/mml:mi>\n        <\/mml:mrow>\n      <\/mml:msup>\n      <mml:mo stretchy=\"false\">)<\/mml:mo>\n    <\/mml:mrow>\n    <mml:annotation encoding=\"application\/x-tex\">\\mathcal {O}(h^{2k+m})<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> in the negative-order norm. By post-processing the LDG solution to a linear convection equation using a specially designed kernel such as the one by Cockburn et al., we can compute this same order accuracy in the <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"upper L squared\">\n  <mml:semantics>\n    <mml:msup>\n      <mml:mi>L<\/mml:mi>\n      <mml:mn>2<\/mml:mn>\n    <\/mml:msup>\n    <mml:annotation encoding=\"application\/x-tex\">L^2<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula>-norm. Additionally, we present numerical studies that confirm that we can improve the LDG solution from <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"script upper O left-parenthesis h Superscript k plus 1 Baseline right-parenthesis\">\n  <mml:semantics>\n    <mml:mrow>\n      <mml:mrow class=\"MJX-TeXAtom-ORD\">\n        <mml:mi class=\"MJX-tex-caligraphic\" mathvariant=\"script\">O<\/mml:mi>\n      <\/mml:mrow>\n      <mml:mo stretchy=\"false\">(<\/mml:mo>\n      <mml:msup>\n        <mml:mi>h<\/mml:mi>\n        <mml:mrow class=\"MJX-TeXAtom-ORD\">\n          <mml:mi>k<\/mml:mi>\n          <mml:mo>+<\/mml:mo>\n          <mml:mn>1<\/mml:mn>\n        <\/mml:mrow>\n      <\/mml:msup>\n      <mml:mo stretchy=\"false\">)<\/mml:mo>\n    <\/mml:mrow>\n    <mml:annotation encoding=\"application\/x-tex\">\\mathcal {O}(h^{k+1})<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> to <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"script upper O left-parenthesis h Superscript 2 k plus 1 Baseline right-parenthesis\">\n  <mml:semantics>\n    <mml:mrow>\n      <mml:mrow class=\"MJX-TeXAtom-ORD\">\n        <mml:mi class=\"MJX-tex-caligraphic\" mathvariant=\"script\">O<\/mml:mi>\n      <\/mml:mrow>\n      <mml:mo stretchy=\"false\">(<\/mml:mo>\n      <mml:msup>\n        <mml:mi>h<\/mml:mi>\n        <mml:mrow class=\"MJX-TeXAtom-ORD\">\n          <mml:mn>2<\/mml:mn>\n          <mml:mi>k<\/mml:mi>\n          <mml:mo>+<\/mml:mo>\n          <mml:mn>1<\/mml:mn>\n        <\/mml:mrow>\n      <\/mml:msup>\n      <mml:mo stretchy=\"false\">)<\/mml:mo>\n    <\/mml:mrow>\n    <mml:annotation encoding=\"application\/x-tex\">\\mathcal {O}(h^{2k+1})<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> using alternating fluxes and that we actually obtain <inline-formula content-type=\"math\/mathml\">\n<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" alttext=\"script upper O left-parenthesis h Superscript 2 k plus 2 Baseline right-parenthesis\">\n  <mml:semantics>\n    <mml:mrow>\n      <mml:mrow class=\"MJX-TeXAtom-ORD\">\n        <mml:mi class=\"MJX-tex-caligraphic\" mathvariant=\"script\">O<\/mml:mi>\n      <\/mml:mrow>\n      <mml:mo stretchy=\"false\">(<\/mml:mo>\n      <mml:msup>\n        <mml:mi>h<\/mml:mi>\n        <mml:mrow class=\"MJX-TeXAtom-ORD\">\n          <mml:mn>2<\/mml:mn>\n          <mml:mi>k<\/mml:mi>\n          <mml:mo>+<\/mml:mo>\n          <mml:mn>2<\/mml:mn>\n        <\/mml:mrow>\n      <\/mml:msup>\n      <mml:mo stretchy=\"false\">)<\/mml:mo>\n    <\/mml:mrow>\n    <mml:annotation encoding=\"application\/x-tex\">\\mathcal {O}(h^{2k+2})<\/mml:annotation>\n  <\/mml:semantics>\n<\/mml:math>\n<\/inline-formula> for diffusion-dominated problems.<\/p>","DOI":"10.1090\/s0025-5718-2012-02586-5","type":"journal-article","created":{"date-parts":[[2012,3,5]],"date-time":"2012-03-05T13:54:28Z","timestamp":1330955668000},"page":"1929-1950","source":"Crossref","is-referenced-by-count":37,"title":["Accuracy-enhancement of discontinuous Galerkin solutions for convection-diffusion equations in multiple-dimensions"],"prefix":"10.1090","volume":"81","author":[{"given":"Liangyue","family":"Ji","sequence":"first","affiliation":[]},{"given":"Yan","family":"Xu","sequence":"additional","affiliation":[]},{"given":"Jennifer","family":"Ryan","sequence":"additional","affiliation":[]}],"member":"14","published-online":{"date-parts":[[2012,3,2]]},"reference":[{"key":"1","doi-asserted-by":"publisher","first-page":"5","DOI":"10.1007\/s10915-004-4133-9","article-title":"Superconvergence of discontinuous finite element solutions for transient convection-diffusion problems","volume":"22\/23","author":"Adjerid, Slimane","year":"2005","journal-title":"J. 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