From d5ac4fc67fde44bd0c5e02df8e83033f9d716e59 Mon Sep 17 00:00:00 2001
From: Chulwoo Jung <chulwoo@bnl.gov>
Date: Wed, 26 Nov 2025 22:13:27 +0000
Subject: [PATCH] Starting to modified KS

---
 Grid/algorithms/iterative/KrylovSchur.h | 34 +++++++++++++++++--------
 examples/Example_krylov_schur.cc        | 26 ++++++++++---------
 2 files changed, 37 insertions(+), 23 deletions(-)

diff --git a/Grid/algorithms/iterative/KrylovSchur.h b/Grid/algorithms/iterative/KrylovSchur.h
index d5bf6a20..a83983dc 100644
--- a/Grid/algorithms/iterative/KrylovSchur.h
+++ b/Grid/algorithms/iterative/KrylovSchur.h
@@ -89,6 +89,14 @@ struct ComplexComparator
   RitzFilter RF;
   ComplexComparator (RitzFilter _rf) : RF(_rf) {}
   bool operator()(std::complex<double> z1, std::complex<double> z2) { 
+      RealD tmp1, tmp2;
+      tmp1=std::abs(std::imag(z1));
+      tmp2=std::abs(std::imag(z2));
+//      if ( std::abs(std::real(z1)) <0.76) tmp1 +=4.;
+//      if ( std::abs(std::real(z2)) <0.76) tmp2 +=4.;
+      if ( std::abs(std::real(z1)) >2.) tmp1 +=4.;
+      if ( std::abs(std::real(z2)) >2.) tmp2 +=4.;
+
     switch (RF) {
       case EvalNormSmall:
         return std::abs(z1) < std::abs(z2);
@@ -103,9 +111,11 @@ struct ComplexComparator
       case EvalImLarge:
         return std::imag(z1) > std::imag(z2);
       case EvalImNormSmall:
-        return std::abs(std::imag(z1)) < std::abs(std::imag(z2));
+	return tmp1 < tmp2;
+//        return std::abs(std::imag(z1)) < std::abs(std::imag(z2));
       case EvalImNormLarge:
-        return std::abs(std::imag(z1)) > std::abs(std::imag(z2));
+	return tmp1 > tmp2;
+//        return std::abs(std::imag(z1)) > std::abs(std::imag(z2));
       default:
         assert(0);
     }
@@ -224,8 +234,8 @@ class ComplexSchurDecomposition {
      */
     // void schurReorder(int Nk, std::function compare) {
     int schurReorder(int Nk) {
-      for (int i = 0; i < Nm; i++) {
-        for (int k = 0; k <= Nm - 2; k++) {
+      for (int i = 0; i < Nk; i++) {
+        for (int k = 0; k <= Nm - 2-i ; k++) {
           int idx = Nm - 2 - k;
           // TODO use RitzFilter enum here
           // if (std::abs(S(idx, idx)) < std::abs(S(idx+1, idx+1))) {            // sort by largest modulus of eigenvalue
@@ -235,10 +245,10 @@ class ComplexSchurDecomposition {
           }
         }
       }
-      int temp=1;
-      for (int i = 0; i < Nm-1; i++) {
+      int temp=Nk/2;
+      for (int i = temp; i < Nk; i++) {
         std::cout << GridLogMessage << "S " << i << " "<<std::real(S(i,i))<<" "<<std::imag(S(i,i)) << std::endl;
-	if (std::abs(std::imag(S(i,i))< 0.01)) temp= i+1;
+	if (std::abs(std::imag(S(i,i)))< 0.01) temp= i+1;
       }
       return temp;
     }
@@ -341,13 +351,13 @@ class KrylovSchur {
       int start = 0;
       Field startVec = v0;
       littleEvecs = Eigen::MatrixXcd::Zero(Nm, Nm);
+      int Nconv=Nstop;
       for (int i = 0; i < MaxIter; i++) {
         std::cout << GridLogMessage << "Restart Iteration " << i << std::endl;
 
         // Perform Arnoldi steps to compute Krylov basis and Rayleigh quotient (Hess)
         arnoldiIteration(startVec, Nm, start, doubleOrthog);
         startVec = u;        // original code
-        start = Nk;
 
         // checkKSDecomposition();
 
@@ -359,7 +369,10 @@ class KrylovSchur {
         // Rearrange Schur matrix so wanted evals are on top left (like MATLAB's ordschur)
         std::cout << GridLogMessage << "Reordering Schur eigenvalues Nk=" << Nk << std::endl;
 //        Nk=schur.schurReorder(_Nk);
-        schur.schurReorder(Nk);
+//        start = Nk;
+        schur.schurReorder(_Nk);
+	Nk = (Nconv+_Nk)/2;
+	start=Nk;
 	std::cout << GridLogMessage << "After Reorder Nk= "<<Nk<<std::endl;
         Eigen::MatrixXcd Q = schur.getMatrixQ();
         Qt = Q.adjoint();                           // TODO should Q be real?
@@ -414,7 +427,7 @@ class KrylovSchur {
         std::cout << GridLogMessage << "Eigenvalues (first Nk sorted): " << std::endl << evals << std::endl;
 
         // check convergence and return if needed. 
-        int Nconv = converged();
+        Nconv = converged();
         std::cout << GridLogMessage << "Number of evecs converged: " << Nconv << std::endl;
         if (Nconv >= Nstop || i == MaxIter - 1) {
           std::cout << GridLogMessage << "Converged with " << Nconv << " / " << Nstop << " eigenvectors on iteration " 
@@ -469,7 +482,6 @@ class KrylovSchur {
         u = Zero();
       } else {
         std::cout << GridLogMessage << "start= " <<start<< " basis.size= "<<basis.size()<<std::endl;
-//        assert( start <= basis.size() );      // should be starting at the end of basis (start = Nk)
         // assert( start == basis.size() );      // should be starting at the end of basis (start = Nk)
         std::cout << GridLogMessage << "Resetting Rayleigh and b" << std::endl;
         Eigen::MatrixXcd RayleighCp = Rayleigh;
diff --git a/examples/Example_krylov_schur.cc b/examples/Example_krylov_schur.cc
index 6721eaa6..ffc85e27 100644
--- a/examples/Example_krylov_schur.cc
+++ b/examples/Example_krylov_schur.cc
@@ -51,6 +51,7 @@ struct LanczosParameters: Serializable {
                                 Integer, Nk,
                                 Integer, Np,
                                 Integer, ReadEvec,
+                                Integer, maxIter,
 	  			RealD, resid,
 	  			RealD, ChebyLow,
 	  			RealD, ChebyHigh,
@@ -453,18 +454,6 @@ int main (int argc, char ** argv)
     write(HMCwr,"LanczosParameters",LanParams);
   }
 
-#if 0
-  if(LanParams.ReadEvec) {
-    std::string evecs_file="evec_in";
-    std::cout << GridLogIRL<< "Reading evecs from "<<evecs_file<<std::endl;
-    emptyUserRecord record;
-    Grid::ScidacReader RD;
-    RD.open(evecs_file);
-    RD.readScidacFieldRecord(src,record);
-    RD.close();
-  }
-#endif
-
 
   RealD mass=0.01;
   RealD M5=1.8;
@@ -521,11 +510,24 @@ int main (int argc, char ** argv)
   Nstop=LanParams.Nstop;
   Nk=LanParams.Nk;
   Np=LanParams.Np;
+  maxIter=LanParams.maxIter;
   Nm = Nk + Np;
   int Nu=16;
   std::vector<LatticeFermion> src(Nu,FGrid); 
   for(int i=0;i<Nu;i++) random(RNG5,src[i]);
 
+#if 1
+  if(LanParams.ReadEvec) {
+    std::string evecs_file="evec_in";
+    std::cout << GridLogIRL<< "Reading evecs from "<<evecs_file<<std::endl;
+    emptyUserRecord record;
+    Grid::ScidacReader RD;
+    RD.open(evecs_file);
+    RD.readScidacFieldRecord(src[0],record);
+    RD.close();
+  }
+#endif
+
   Coordinate origin ({0,0,0,0});
   auto tmpSrc = peekSite(src[0], origin);
   std::cout << "[DEBUG] Source at origin = " <<  tmpSrc << std::endl;