From 2326b07c681b3c859d37e3823c82218b4f034d5e Mon Sep 17 00:00:00 2001
From: Ray Speth <speth@mit.edu>
Date: Fri, 12 Apr 2013 23:06:05 +0000
Subject: [PATCH] [1D] Reset timestep after grid refinement

This addresses a performance issue where many failed timesteps would be
taken after adding new grid points. These failed timesteps are slow because
they require additional Jacobian re-evaluations. It is more efficient to
preemptively reduce the time step after adding new grid points.

Resolves Issue 155.
---
 src/oneD/Sim1D.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/oneD/Sim1D.cpp b/src/oneD/Sim1D.cpp
index c902f0fd1..a3a9e5dbe 100644
--- a/src/oneD/Sim1D.cpp
+++ b/src/oneD/Sim1D.cpp
@@ -365,6 +365,11 @@ void Sim1D::solve(int loglevel, bool refine_grid)
 
         if (refine_grid) {
             new_points = refine(loglevel);
+            if (new_points) {
+                // If the grid has changed, preemptively reduce the timestep
+                // to avoid multiple successive failed time steps.
+                dt = m_tstep;
+            }
             if (new_points && loglevel > 6) {
                 save("debug_sim1d.xml", "debug", "After regridding");
             }