From d6acf643e41a399f4a4e678eeceda2a8a54156cd Mon Sep 17 00:00:00 2001
From: Johannes Terblanche <6612981+Affie@users.noreply.github.com>
Date: Tue, 17 Oct 2023 15:04:15 +0200
Subject: [PATCH] Only compute Jacobian in RLM if last step success (#303)

Co-authored-by: Johannes Terblanche <Affie@users.noreply.github.com>
---
 src/plans/nonlinear_least_squares_plan.jl | 2 ++
 src/solvers/LevenbergMarquardt.jl         | 7 ++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/plans/nonlinear_least_squares_plan.jl b/src/plans/nonlinear_least_squares_plan.jl
index d517ffa058..9d8a3bcbf5 100644
--- a/src/plans/nonlinear_least_squares_plan.jl
+++ b/src/plans/nonlinear_least_squares_plan.jl
@@ -192,6 +192,7 @@ mutable struct LevenbergMarquardtState{
     damping_term_min::Tparams
     β::Tparams
     expect_zero_residual::Bool
+    last_step_successful::Bool
     function LevenbergMarquardtState(
         M::AbstractManifold,
         p::P,
@@ -244,6 +245,7 @@ mutable struct LevenbergMarquardtState{
             damping_term_min,
             β,
             expect_zero_residual,
+            true,
         )
     end
 end
diff --git a/src/solvers/LevenbergMarquardt.jl b/src/solvers/LevenbergMarquardt.jl
index 56674b5b2f..e89fd37d35 100644
--- a/src/solvers/LevenbergMarquardt.jl
+++ b/src/solvers/LevenbergMarquardt.jl
@@ -264,7 +264,10 @@ function step_solver!(
     M = get_manifold(dmp)
     nlso = get_objective(dmp)
     basis_ox = _maybe_get_basis(M, lms.p, nlso.jacobian_tangent_basis)
-    get_jacobian!(dmp, lms.jacF, lms.p, basis_ox)
+    # a new Jacobian is only  needed if the last step was successful
+    if lms.last_step_successful
+        get_jacobian!(dmp, lms.jacF, lms.p, basis_ox)
+    end
     λk = lms.damping_term * norm(lms.residual_values)^2
 
     JJ = transpose(lms.jacF) * lms.jacF + λk * I
@@ -292,8 +295,10 @@ function step_solver!(
         if lms.expect_zero_residual
             lms.damping_term = max(lms.damping_term_min, lms.damping_term / lms.β)
         end
+        lms.last_step_successful = true
     else
         lms.damping_term *= lms.β
+        lms.last_step_successful = false
     end
     return lms
 end