From: Marc Fehling <mafehling.git@gmail.com>
Date: Wed, 6 Jan 2021 04:14:59 +0000 (-0700)
Subject: Adjusted settings for default FESeries::Legendre object.
X-Git-Tag: v9.3.0-rc1~656^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ae7369673f008785f06a1757dd20ee926973d5cb;p=dealii.git

Adjusted settings for default FESeries::Legendre object.
---

diff --git a/include/deal.II/numerics/smoothness_estimator.h b/include/deal.II/numerics/smoothness_estimator.h
index 7aa7200d62..b0d11b6531 100644
--- a/include/deal.II/numerics/smoothness_estimator.h
+++ b/include/deal.II/numerics/smoothness_estimator.h
@@ -228,10 +228,10 @@ namespace SmoothnessEstimator
      * the default configuration for smoothness estimation purposes.
      *
      * For each finite element of the provided @p fe_collection, we use as many
-     * modes as its polynomial degree plus one, since we start with the first
-     * Legendre polynomial which is just a constant. Further for each element,
-     * we use a Gaussian quadrature designed to yield exact results for the
-     * highest order Legendre polynomial used.
+     * modes as its polynomial degree plus two. This includes the first Legendre
+     * polynomial which is just a constant. Further for each element, we use a
+     * Gaussian quadrature designed to yield exact results for the highest order
+     * Legendre polynomial used.
      */
     template <int dim, int spacedim>
     FESeries::Legendre<dim, spacedim>
diff --git a/source/numerics/smoothness_estimator.cc b/source/numerics/smoothness_estimator.cc
index 82c651701c..fa7c0c3c41 100644
--- a/source/numerics/smoothness_estimator.cc
+++ b/source/numerics/smoothness_estimator.cc
@@ -290,9 +290,13 @@ namespace SmoothnessEstimator
     default_fe_series(const hp::FECollection<dim, spacedim> &fe_collection)
     {
       // Default number of coefficients per direction.
+      //
+      // With a number of modes equal to the polynomial degree plus two for each
+      // finite element, the smoothness estimation algorithm tends to produce
+      // stable results.
       std::vector<unsigned int> n_coefficients_per_direction;
       for (unsigned int i = 0; i < fe_collection.size(); ++i)
-        n_coefficients_per_direction.push_back(fe_collection[i].degree + 1);
+        n_coefficients_per_direction.push_back(fe_collection[i].degree + 2);
 
       // Default quadrature collection.
       //