From: Wolfgang Bangerth Date: Mon, 16 Aug 2021 23:53:09 +0000 (-0600) Subject: Update documentation of FE_Q constructor. X-Git-Tag: v9.4.0-rc1~1068^2 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F12661%2Fhead;p=dealii.git Update documentation of FE_Q constructor. --- diff --git a/include/deal.II/fe/fe_q.h b/include/deal.II/fe/fe_q.h index b77dcef2f6..f451b7df8d 100644 --- a/include/deal.II/fe/fe_q.h +++ b/include/deal.II/fe/fe_q.h @@ -559,11 +559,16 @@ public: * Constructor for tensor product polynomials with support points @p points * based on a one-dimensional quadrature formula. The degree of the finite * element is points.size()-1. Note that the first point has to be - * 0 and the last one 1. Constructing + * 0 and the last one 1, to ensure that the resulting element is continuous. + * As a consequence, only *certain* quadrature formulas make sense as + * argument to this constructor. Specifically, constructing * FE_Q(QGaussLobatto<1>(fe_degree+1)) is equivalent to the * constructor that specifies the polynomial degree only. For selecting - * equidistant nodes at fe_degree > 2, construct - * FE_Q(QIterated<1>(QTrapezoid<1>(),fe_degree)). + * equidistant nodes at fe_degree > 2, use + * FE_Q(QIterated<1>(QTrapezoid<1>(),fe_degree)), though the + * use of equidistant node points is known to lead to poorly conditioned + * linear systems with poor interpolation properties for high polynomial + * degrees (which is why the default uses the QGaussLobatto points). * * The *space* created by this constructor is the * same as if you had called `FE_Q(points.size()-1)`, but what *is*