Do not leave NaN values in output vectors.

doc/modules/changes/20230710_bangerth

@@ -0,0 +1,6 @@
+Fixed:
+When using the 'artificial viscosity' visualization postprocessor in parallel,
+we used to put NaNs into the output vector (for ghost and artificial
+cells) that then triggered floating point exceptions. This is now fixed.
+<br>
+(Wolfgang Bangerth, 2023/07/10)

source/postprocess/visualization/artificial_viscosity.cc

@@ -45,6 +45,19 @@ namespace aspect
         return_value ("artificial_viscosity",
                       new Vector<float>(this->get_triangulation().n_active_cells()));
         this->get_artificial_viscosity(*return_value.second);
+
+        // The function we call above sets the artificial viscosity to
+        // signaling_nan on all artificial cells and, possibly, ghost cells.
+        // This runs into trouble in DataOut that wants to copy this vector
+        // from Vector<float> to Vector<double>, and the conversion trips
+        // up over the NaNs, causing a floating point exception.
+        //
+        // To avoid this, strip out the NaNs and instead set these values
+        // to zero -- we won't be outputting these values anyway.
+        for (const auto &cell : this->get_triangulation().active_cell_iterators())
+          if (cell->is_locally_owned() == false)
+            (*return_value.second)[cell->active_cell_index()] = 0;
+
         return return_value;
       }
     }

tests/composition_active_nans.prm

@@ -0,0 +1,132 @@
+# When using the 'artificial viscosity' viz postprocessor in parallel,
+# we used to put NaNs into the output vector (for ghost and artificial
+# cells) that then triggered floating point exceptions. Check that
+# this no longer happens. For this, all we need to do is get past the
+# first time we create graphical output.
+
+# MPI: 2
+
+set Dimension                              = 2
+set Start time                             = 0
+set End time                               = 0.1
+set Use years in output instead of seconds = false
+
+
+
+subsection Geometry model
+  set Model name = box
+
+  subsection Box
+    set X extent = 2
+    set Y extent = 1
+  end
+end
+
+
+# The parameters below this comment were created by the update script
+# as replacement for the old 'Model settings' subsection. They can be
+# safely merged with any existing subsections with the same name.
+
+subsection Boundary temperature model
+  set Fixed temperature boundary indicators   = 2, 3
+end
+
+subsection Boundary velocity model
+  set Tangential velocity boundary indicators = 0, 1, 2
+end
+
+subsection Boundary velocity model
+  set Prescribed velocity boundary indicators = 3: function
+end
+
+subsection Heating model
+  set List of model names = shear heating
+end
+
+subsection Boundary temperature model
+  set List of model names = box
+
+  subsection Box
+    set Bottom temperature = 1
+    set Top temperature    = 0
+  end
+end
+
+
+subsection Boundary velocity model
+  subsection Function
+    set Variable names      = x,z,t
+    set Function constants  = pi=3.1415926
+    set Function expression = if(x>1+sin(0.5*pi*t), 1, -1); 0
+  end
+end
+
+
+subsection Gravity model
+  set Model name = vertical
+end
+
+
+subsection Initial temperature model
+  set Model name = function
+
+  subsection Function
+    set Variable names      = x,z
+    set Function expression = (1-z)
+  end
+end
+
+
+# Compared to the passive material model, we here make
+# the density composition dependent by letting it depend
+# linearly on the value of the first compositional field.
+subsection Material model
+  set Model name = simple
+
+  subsection Simple model
+    set Thermal conductivity                           = 1e-6
+    set Thermal expansion coefficient                  = 0.01
+    set Viscosity                                      = 1
+    set Reference density                              = 1
+    set Reference temperature                          = 0
+    set Density differential for compositional field 1 = 100
+  end
+end
+
+
+subsection Mesh refinement
+  set Initial adaptive refinement        = 0
+  set Initial global refinement          = 3
+  set Time steps between mesh refinement = 0
+end
+
+
+subsection Postprocess
+  set List of postprocessors = visualization, temperature statistics, composition statistics
+
+  subsection Visualization
+    set Interpolate output = false
+    set List of output variables = density, artificial viscosity
+    set Time between graphical output = 0.1
+  end
+end
+
+
+# This is the new part: We declare that there will
+# be two compositional fields that will be
+# advected along. Their initial conditions are given by
+# a function that is one for the lowermost 0.2 height
+# units of the domain and zero otherwise in the first case,
+# and one in the top most 0.2 height units in the latter.
+subsection Compositional fields
+  set Number of fields = 2
+end
+
+subsection Initial composition model
+  set Model name = function
+
+  subsection Function
+    set Variable names      = x,y
+    set Function expression = if(y<0.2, 1, 0) ; if(y>0.8, 1, 0)
+  end
+end

tests/composition_active_nans/screen-output

@@ -0,0 +1,52 @@
+-----------------------------------------------------------------------------
+-----------------------------------------------------------------------------
+
+-----------------------------------------------------------------------------
+-----------------------------------------------------------------------------
+Number of active cells: 64 (on 4 levels)
+Number of degrees of freedom: 1,526 (578+81+289+289+289)
+
+*** Timestep 0:  t=0 seconds, dt=0 seconds
+   Solving temperature system... 0 iterations.
+   Solving C_1 system ... 0 iterations.
+   Solving C_2 system ... 0 iterations.
+   Rebuilding Stokes preconditioner...
+   Solving Stokes system... 17+0 iterations.
+
+   Postprocessing:
+     Writing graphical output:  output-composition_active_nans/solution/solution-00000
+     Temperature min/avg/max:   0 K, 0.5 K, 1 K
+     Compositions min/max/mass: 0/1/0.4583 // 0/1/0.4583
+
+*** Timestep 1:  t=0.0625 seconds, dt=0.0625 seconds
+   Solving temperature system... 10 iterations.
+   Solving C_1 system ... 11 iterations.
+   Solving C_2 system ... 12 iterations.
+   Rebuilding Stokes preconditioner...
+   Solving Stokes system... 14+0 iterations.
+
+   Postprocessing:
+     Temperature min/avg/max:   0 K, 0.5013 K, 1 K
+     Compositions min/max/mass: -0.006514/1.046/0.4591 // -0.01597/1.028/0.4583
+
+*** Timestep 2:  t=0.1 seconds, dt=0.0375 seconds
+   Solving temperature system... 10 iterations.
+   Solving C_1 system ... 12 iterations.
+   Solving C_2 system ... 12 iterations.
+   Rebuilding Stokes preconditioner...
+   Solving Stokes system... 17+0 iterations.
+
+   Postprocessing:
+     Writing graphical output:  output-composition_active_nans/solution/solution-00001
+     Temperature min/avg/max:   0 K, 0.5021 K, 1 K
+     Compositions min/max/mass: -0.008189/1.059/0.4595 // -0.02059/1.033/0.4583
+
+Termination requested by criterion: end time
+
+
++----------------------------------------------+------------+------------+
++----------------------------------+-----------+------------+------------+
++----------------------------------+-----------+------------+------------+
+
+-----------------------------------------------------------------------------
+-----------------------------------------------------------------------------