From 72b8366c3387f78939660b4dc1629fc43ae8e83c Mon Sep 17 00:00:00 2001
From: Remi Lehe <remi.lehe@normalesup.org>
Date: Fri, 28 Aug 2026 02:14:25 -0700
Subject: [PATCH] Remove unused GMRES option in curl-curl MLMG preconditioner

The curl-curl preconditioner had an undocumented option to use GMRES
(optionally preconditioned by MLMG) instead of MLMG directly, i.e. GMRES
as a preconditioner inside the outer GMRES solver. This was never used
in practice and was not documented, so remove it along with the parsing
of pc_curl_curl_mlmg.use_gmres and pc_curl_curl_mlmg.use_gmres_pc.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 Source/NonlinearSolvers/CurlCurlMLMGPC.H | 32 +++---------------------
 1 file changed, 4 insertions(+), 28 deletions(-)

diff --git a/Source/NonlinearSolvers/CurlCurlMLMGPC.H b/Source/NonlinearSolvers/CurlCurlMLMGPC.H
index 506df3a9b5f..514d97a1b7a 100644
--- a/Source/NonlinearSolvers/CurlCurlMLMGPC.H
+++ b/Source/NonlinearSolvers/CurlCurlMLMGPC.H
@@ -23,7 +23,6 @@
 #include <AMReX_MLLinOp.H>
 #include <AMReX_MLCurlCurl.H>
 #include <AMReX_MLMG.H>
-#include <AMReX_GMRES_MLMG.H>
 
 /**
  * \brief Curl-curl Preconditioner
@@ -114,8 +113,6 @@ class CurlCurlMLMGPC : public Preconditioner<T,Ops>
         bool m_bottom_verbose = false;
         bool m_agglomeration = true;
         bool m_consolidation = true;
-        bool m_use_gmres = false;
-        bool m_use_gmres_pc = true;
 
         int m_max_iter = 1;
         int m_max_coarsening_level = 30;
@@ -143,7 +140,6 @@ class CurlCurlMLMGPC : public Preconditioner<T,Ops>
         std::unique_ptr<amrex::LPInfo> m_info;
         std::unique_ptr<amrex::MLCurlCurl> m_curl_curl;
         std::unique_ptr<amrex::MLMGT<MFArr>> m_solver;
-        std::unique_ptr<amrex::GMRESMLMGT<MFArr>> m_gmres_solver;
 
         /**
          * \brief Read parameters
@@ -168,12 +164,6 @@ void CurlCurlMLMGPC<T,Ops>::printParameters() const
     Print() << pc_name << " max_coarsening_level: " << m_max_coarsening_level << "\n";
     Print() << pc_name << " absolute tolerance:   " << m_atol << "\n";
     Print() << pc_name << " relative tolerance:   " << m_rtol << "\n";
-    Print() << pc_name << " use GMRES:            " << (m_use_gmres?"true":"false") << "\n";
-    if (m_use_gmres) {
-        Print() << pc_name
-                << " use PC for GMRES:     "
-                << (m_use_gmres_pc?"true":"false") << "\n";
-    }
 }
 
 template <class T, class Ops>
@@ -188,8 +178,6 @@ void CurlCurlMLMGPC<T,Ops>::readParameters()
     pp.query("max_coarsening_level", m_max_coarsening_level);
     pp.query("absolute_tolerance",  m_atol);
     pp.query("relative_tolerance",  m_rtol);
-    pp.query("use_gmres",  m_use_gmres);
-    pp.query("use_gmres_pc",  m_use_gmres_pc);
 }
 
 template <class T, class Ops>
@@ -252,14 +240,6 @@ void CurlCurlMLMGPC<T,Ops>::Define ( const T& a_U,
     m_solver->setVerbose(static_cast<int>(m_verbose));
     m_solver->setBottomVerbose(static_cast<int>(m_bottom_verbose));
 
-    // If using GMRES solver, construct it
-    if (m_use_gmres) {
-        m_gmres_solver = std::make_unique<GMRESMLMGT<MFArr>>(*m_solver);
-        m_gmres_solver->usePrecond(m_use_gmres_pc);
-        m_gmres_solver->setPrecondNumIters(m_max_iter);
-        m_gmres_solver->setVerbose(static_cast<int>(m_verbose));
-    }
-
     m_bcoefs = m_ops->GetMassMatricesCoeff();
     if (m_bcoefs != nullptr) { m_beta_scalar = false; }
 
@@ -390,14 +370,10 @@ void CurlCurlMLMGPC<T,Ops>::Apply (T& a_x, const T& a_b)
 #endif
 
         m_curl_curl->prepareRHS({&rhs});
-        if (m_use_gmres) {
-            m_gmres_solver->solve(solution, rhs, m_rtol, m_atol);
-        } else {
-            // m_rtol and m_atol are zero by default: this ensures that MLMG performs a fixed
-            // number of iterations (m_max_iter V-cycles), for any right-hand side, so that the
-            // preconditioner is a fixed linear operator, as required by GMRES.
-            m_solver->solve({&solution}, {&rhs}, m_rtol, m_atol);
-        }
+        // m_rtol and m_atol are zero by default: this ensures that MLMG performs a fixed
+        // number of iterations (m_max_iter V-cycles), for any right-hand side, so that the
+        // preconditioner is a fixed linear operator, as required by GMRES.
+        m_solver->solve({&solution}, {&rhs}, m_rtol, m_atol);
     }
 }