MPI for 2D parabolic system on conforming P4est mesh (#2886)

* enabled MPI for 2D parabolic system on P4est mesh (from present main)

* adapted naming: viscous -> parabolic

* added assertion to ensure no mortars are present

* cleanup style

* increased allocation limit (checked similar allocations in MPI as hyperbolic communication, now just 3 x communication)

* Apply suggestions from code review

Removed dispatch to unsupoorted T8codeMeshParallel

Co-authored-by: Daniel Doehring <doehringd2@gmail.com>

* added comments to clarify sign-flip

* extended comment on orientation_factor

* renamed surface integral MPI accumulate

* Apply suggestions from code review

adhere to mpi internal functions

Co-authored-by: Hendrik Ranocha <ranocha@users.noreply.github.com>

* removed unnecessary function

* moved mpi send to end

* Apply suggestions from code review

applied suggested comment improvments

Co-authored-by: Daniel Doehring <doehringd2@gmail.com>

* formatting applied

* added name to Authors

* Apply suggestions from code review

* Update src/solvers/dgsem_p4est/dg_2d_parabolic_parallel.jl

---------

Co-authored-by: TJP-Karpowski <MessageInGitHubPlease>
Co-authored-by: Daniel Doehring <doehringd2@gmail.com>
Co-authored-by: Hendrik Ranocha <ranocha@users.noreply.github.com>
Co-authored-by: Michael Schlottke-Lakemper <michael@sloede.com>

Author: 4 people

AUTHORS.md

@@ -37,6 +37,7 @@ are listed in alphabetical order:
 * Gregor Gassner
 * Lucas Gemein
 * Sven Goldberg
+* T. Jeremy P. Karpowski
 * Joshua Lampert
 * Tristan Montoya
 * Julia Odenthal

src/callbacks_step/analysis_surface_integral_2d.jl

@@ -250,6 +250,9 @@ function analyze(surface_variable::AnalysisSurfaceIntegral, du, u, t,
             j_node += j_node_step
         end
     end
+    if mpi_isparallel()
+        surface_integral = MPI.Allreduce!(Ref(surface_integral), +, mpi_comm())[]
+    end
     return surface_integral
 end
 
@@ -320,6 +323,9 @@ function analyze(surface_variable::AnalysisSurfaceIntegral{Variable}, du, u, t,
             j_node += j_node_step
         end
     end
+    if mpi_isparallel()
+        surface_integral = MPI.Allreduce!(Ref(surface_integral), +, mpi_comm())[]
+    end
     return surface_integral
 end
 end # muladd