From 1731cc0ae122dd22d437093937a29856a710ab16 Mon Sep 17 00:00:00 2001
From: Klaus <kweide@users.noreply.github.com>
Date: Mon, 28 Sep 2020 17:45:46 -0500
Subject: [PATCH] Revert "NodalProjector: fix comments (#1396)"

This reverts commit fe8548adf7fd3452dde919444b54b43381eff32e.
---
 .../Projections/AMReX_NodalProjector.H        | 27 +++----------------
 .../Projections/AMReX_NodalProjector.cpp      |  6 ++---
 2 files changed, 7 insertions(+), 26 deletions(-)

diff --git a/Src/LinearSolvers/Projections/AMReX_NodalProjector.H b/Src/LinearSolvers/Projections/AMReX_NodalProjector.H
index a2c77b0cd84..209e6c53436 100644
--- a/Src/LinearSolvers/Projections/AMReX_NodalProjector.H
+++ b/Src/LinearSolvers/Projections/AMReX_NodalProjector.H
@@ -7,9 +7,6 @@
 #include <AMReX_MLNodeLaplacian.H>
 #include <AMReX_MLMG.H>
 
-//
-//
-// ***************************  DEFAULT MODE  ***************************
 //
 // Solves
 //
@@ -17,31 +14,15 @@
 //
 // and  performs the projection
 //
-//     vel = vel - sigma * grad(phi)
+//     vel = vel - ( sigma / alpha ) * grad(phi)
 //
-// vel, sigma, and S_cc are cell-centered variables, while
+// vel, sigma, alpha, and S_cc are cell-centered variables, while
 // phi and S_nd are nodal-centered variables.
 //
-// ***************************  CUSTOM MODE   ***************************
-//
-// Solves
-//
-//     div(sigma*grad(phi)) = rhs
-//
-// and performs the projection
-//
-//     vel = vel - (sigma/alpha) * grad(phi)
-//
-// alpha is a cell-centered variable, while rhs is nodal-centered.
-//
-// In this mode, the user provides rhs and alpha
-//
 // By default alpha is assumed to be 1. Use setAlpha to change the default.
 //
-// Use setCustomRHS to provide a custom RHS, else "div(vel) + S_nd + S_cc"
-// is used.
-//
-// Example: rhs = div(alpha*vel)
+// The user can provide a custom RHS instead of letting NodalProjector to compute
+// one. Use setCustomRHS to provide a custom RHS.
 //
 namespace amrex {
 
diff --git a/Src/LinearSolvers/Projections/AMReX_NodalProjector.cpp b/Src/LinearSolvers/Projections/AMReX_NodalProjector.cpp
index ad3df2ec41c..db0773d5738 100644
--- a/Src/LinearSolvers/Projections/AMReX_NodalProjector.cpp
+++ b/Src/LinearSolvers/Projections/AMReX_NodalProjector.cpp
@@ -241,7 +241,7 @@ NodalProjector::project ( Real a_rtol, Real a_atol )
     // phi comes out already averaged-down and ready to be used by caller if needed
     m_mlmg -> solve( GetVecOfPtrs(m_phi), GetVecOfConstPtrs(m_rhs), a_rtol, a_atol );
 
-    // Get fluxes -- fluxes = - sigma * grad(phi)
+    // Get fluxes -- fluxes = -  (alpha/beta) * grad(phi)
     m_mlmg -> getFluxes( GetVecOfPtrs(m_fluxes) );
 
     // At this time, the fluxes are "correct" only on regions not covered by finer grids.
@@ -258,7 +258,7 @@ NodalProjector::project ( Real a_rtol, Real a_atol )
     {
         if (m_has_alpha)
         {
-            // fluxes -> fluxes/alpha = - ( sigma / alpha ) * grad(phi)
+            // fluxes -> fluxes/alpha = -grad(phi)/beta
             for (int n = 0; n < AMREX_SPACEDIM; ++n)
             {
                 MultiFab::Divide( m_fluxes[lev], *m_alpha[lev], 0, n, 1, 0 );
@@ -266,7 +266,7 @@ NodalProjector::project ( Real a_rtol, Real a_atol )
         }
 
         //
-        // vel = vel + fluxes = vel - ( sigma / alpha ) * grad(phi)
+        // vel = vel + fluxes = vel - grad(phi) / beta
         //
         // Since we already averaged-down the velocity field and -grad(phi),
         // we perform the projection by simply adding the two of them.