[dune-pdelab] artifact in DiscreteGridfunctionGradient in parallel run

[Jö Fahlke]

Here is the output produced by the program and a screenshot of the defect.  It
shows the x-component of the gradient, which is perpendicular to the partition
boundary.  Not that on right partition, the x-value of the gradient seem to
have been copied from the first interior vertex to the closest border vertex.

Regards,
Jö.

-- 
Jorrit (Jö) Fahlke, Institute for Computational und Applied Mathematics,
University of Münster, Orleans-Ring 10, D-48149 Münster
Tel: +49 251 83 35146 Fax: +49 251 83 32729

Kiss a non-smoker; taste the difference.
-- fortune
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<?xml version="1.0"?>
<VTKFile type="PUnstructuredGrid" version="0.1" byte_order="LittleEndian">
  <PUnstructuredGrid GhostLevel="0">
    <PPointData Scalars="field" Vectors="gradient">
      <PDataArray type="Float32" Name="field" NumberOfComponents="1"/>
      <PDataArray type="Float32" Name="gradient" NumberOfComponents="3"/>
    </PPointData>
    <PCellData>
    </PCellData>
    <PPoints>
      <PDataArray type="Float32" Name="Coordinates" NumberOfComponents="3"/>
    </PPoints>
    <Piece  Source="s0002-p0000-output-00000.vtu"/>
    <Piece  Source="s0002-p0001-output-00000.vtu"/>
  </PUnstructuredGrid>
</VTKFile>
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