From 8c6bcddbabbf64a0a021b17cf8c07581b9340a92 Mon Sep 17 00:00:00 2001
From: Peter Boyle <paboyle@ph.ed.ac.uk>
Date: Mon, 24 Aug 2026 19:40:27 -0400
Subject: [PATCH] Coefficent of GCR printing for poly recording

---
 ...recGeneralisedConjugateResidualNonHermitian.h | 16 ++++++++++++++++
 ...Example_pvdagm_v2_3level_DenseCoarseMatrix.cc |  7 +++++++
 2 files changed, 23 insertions(+)

diff --git a/Grid/algorithms/iterative/PrecGeneralisedConjugateResidualNonHermitian.h b/Grid/algorithms/iterative/PrecGeneralisedConjugateResidualNonHermitian.h
index 5e24a5eb1..8a3bc1ef4 100644
--- a/Grid/algorithms/iterative/PrecGeneralisedConjugateResidualNonHermitian.h
+++ b/Grid/algorithms/iterative/PrecGeneralisedConjugateResidualNonHermitian.h
@@ -72,6 +72,13 @@ public:
   void Level(int n) { Name("Level " + std::to_string(n)); level = n; }
 
   void SetZeroGuess(int z) { ZeroGuess = z; };
+  // Coefficient logging: one line per step with the step length a_k and the
+  // orthogonalisation coefficients b_{k,j}.  These are the data from which a
+  // FIXED polynomial smoother can be harvested: if they are stable from call
+  // to call, the adaptive GCR can be replaced by a stationary p(A) with the
+  // same applies and no reductions.  Off by default; boss rank prints.
+  int  LogCoeffs = 0;
+  void LogCoefficients(int l) { LogCoeffs = l; };
 
   PrecGeneralisedConjugateResidualNonHermitian(RealD tol,Integer maxit,LinearOperatorBase<Field> &_Linop,LinearFunction<Field> &Prec,int _mmax,int _nstep) : 
     Tolerance(tol), 
@@ -229,6 +236,10 @@ public:
 
       cp = axpy_norm(r,-a,q[peri_k],r);
       LinalgTimer.Stop();
+      if ( LogCoeffs ) {
+        GCRLogLevel<<"coeff["<<k<<"] a=("<<real(a)<<","<<imag(a)<<")"
+                   <<" |r|/|r0|="<<sqrt(cp/SSQ)<<std::endl;
+      }
 
       GCRLogLevel<< "PGCR step["<<steps<<"]  resid " << sqrt(cp/SSQ)<<std::endl;
 
@@ -252,6 +263,7 @@ public:
       p[peri_kp]=z;
 
       int northog = ((kp)>(mmax-1))?(mmax-1):(kp);  // if more than mmax done, we orthog all mmax history.
+      std::ostringstream bs;
       for(int back=0;back<northog;back++){
 
 	int peri_back=(k-back)%mmax;   	  GRID_ASSERT((k-back)>=0);
@@ -259,8 +271,12 @@ public:
 	b=-real(innerProduct(q[peri_back],Az))/qq[peri_back];
 	p[peri_kp]=p[peri_kp]+b*p[peri_back];
 	q[peri_kp]=q[peri_kp]+b*q[peri_back];
+        if ( LogCoeffs ) bs<<" b["<<back<<"]="<<b;
 
       }
+      if ( LogCoeffs && northog ) {
+        GCRLogLevel<<"coeff["<<k<<"]"<<bs.str()<<std::endl;
+      }
       qq[peri_kp]=norm2(q[peri_kp]); // could use axpy_norm
       LinalgTimer.Stop();
     }
diff --git a/examples/Example_pvdagm_v2_3level_DenseCoarseMatrix.cc b/examples/Example_pvdagm_v2_3level_DenseCoarseMatrix.cc
index ed5e0ee2b..28b30428c 100644
--- a/examples/Example_pvdagm_v2_3level_DenseCoarseMatrix.cc
+++ b/examples/Example_pvdagm_v2_3level_DenseCoarseMatrix.cc
@@ -108,6 +108,10 @@ int   OuterNstep           = 8;
 // operators default to EXACT.  FineSloppyComms therefore now means
 // "sloppy inside the preconditioner"; =0 makes everything exact.
 int   FineSloppyComms      = 1;
+// SmootherCoeffLog=1 : print the GCR step lengths a_k and orthogonalisation
+// coefficients b_kj of BOTH smoothers every call -- the harvest for a fixed
+// polynomial smoother (stable coefficients => stationary p(A), no reductions).
+int   SmootherCoeffLog     = 0;
 std::function<void(int)> SetFineSloppy = [](int){};
 
 void ParseEnvironment(void)
@@ -125,6 +129,7 @@ void ParseEnvironment(void)
   if(getenv("OuterTol"))           OuterTol           = atof(getenv("OuterTol"));
   if(getenv("OuterMmax"))          OuterMmax          = atoi(getenv("OuterMmax"));
   if(getenv("FineSloppyComms"))    FineSloppyComms    = atoi(getenv("FineSloppyComms"));
+  if(getenv("SmootherCoeffLog"))   SmootherCoeffLog   = atoi(getenv("SmootherCoeffLog"));
   if(getenv("OuterNstep"))         OuterNstep         = atoi(getenv("OuterNstep"));
   if(getenv("LATT")){
     Coordinate l;
@@ -850,6 +855,8 @@ int main (int argc, char ** argv)
 
     FineSmoother_t SmootherGCR(0.0,1,ShiftedPVdagM,simple_fine,FineSmootherOrder,FineSmootherOrder);
     SmootherGCR.Level(1); SmootherGCR.Name("Fsmoother"); SmootherGCR.SetZeroGuess(1);
+    SmootherGCR.LogCoefficients(SmootherCoeffLog);
+    CoarseSmootherGCR.LogCoefficients(SmootherCoeffLog);
 
     MrhsTwoLevelMG<LatticeFermionD,CoarseVector,FineSmoother_t>
       ThreeLevelPrecon(PVdagM, SmootherGCR, MrhsProjector, L2PGCR, Coarse5d, CMrhs);