From d3ce2ace905575654224dbaff320c545467f6aa0 Mon Sep 17 00:00:00 2001
From: Bart de Koning <bart.dekoning@deltares.nl>
Date: Thu, 29 Aug 2024 22:41:16 +0200
Subject: [PATCH] Add check whether relaxation is better than the full step

---
 lib/OrdinaryDiffEqNonlinearSolve/src/newton.jl | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/OrdinaryDiffEqNonlinearSolve/src/newton.jl b/lib/OrdinaryDiffEqNonlinearSolve/src/newton.jl
index c1c8f67db7..d9692406b6 100644
--- a/lib/OrdinaryDiffEqNonlinearSolve/src/newton.jl
+++ b/lib/OrdinaryDiffEqNonlinearSolve/src/newton.jl
@@ -456,8 +456,11 @@ function relax!(dz, nlsolver::AbstractNLSolver, integrator::DEIntegrator, f::TF,
         end
         α0 = one(eltype(ustep))
         ϕ0, dϕ0 = ϕdϕ(zero(α0))
-        α, _ = linesearch(ϕ, dϕ, ϕdϕ, α0, ϕ0, dϕ0)
-        @.. dz = dz * α
+        α, ϕα = linesearch(ϕ, dϕ, ϕdϕ, α0, ϕ0, dϕ0)
+        # Check whether relaxation is better than the full step
+        if ϕα < ϕ(1)
+            @.. dz = dz * α
+        end
         return dz
     end
 end
@@ -510,8 +513,11 @@ function relax(dz, nlsolver::AbstractNLSolver, integrator::DEIntegrator, f::TF,
         end
         α0 = one(eltype(dz))
         ϕ0, dϕ0 = ϕdϕ(zero(α0))
-        α, _ = linesearch(ϕ, dϕ, ϕdϕ, α0, ϕ0, dϕ0)
-        dz = dz * α
+        α, ϕα = linesearch(ϕ, dϕ, ϕdϕ, α0, ϕ0, dϕ0)
+        # Check whether relaxation is better than the full step
+        if ϕα < ϕ(1)
+            dz = dz * α
+        end
         return dz
     end
 end