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Refactording KrylovSchur to have separate operator() for non-shift and shift

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This commit is contained in:
Chulwoo Jung
2026-07-10 17:39:36 -04:00
parent 722d68b0d9
commit f1249685aa
1 changed files with 183 additions and 211 deletions
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Grid/algorithms/iterative/KrylovSchur.h
+127 -155
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@@ -338,12 +338,11 @@ class KrylovSchur {
RitzFilter ritzFilter; // how to sort evals
public:
RealD *shift;
bool doEvalCheck = false;
KrylovSchur(LinearOperatorBase<Field> &_Linop, GridBase *_Grid, RealD _Tolerance, RitzFilter filter = EvalReSmall)
: Linop(_Linop), Grid(_Grid), Tolerance(_Tolerance), ritzFilter(filter), u(_Grid), MaxIter(-1), Nm(-1), Nk(-1), Nstop (-1),
evals (0), ritzEstimates (), evecs (), ssq (0.0), rtol (0.0), beta_k (0.0), approxLambdaMax (0.0),shift(NULL)
evals (0), ritzEstimates (), evecs (), ssq (0.0), rtol (0.0), beta_k (0.0), approxLambdaMax (0.0)
{
u = Zero();
};
@@ -360,17 +359,13 @@ class KrylovSchur {
std::vector<Field> getEvecs() { return evecs; }
/**
* Runs the Krylov-Schur loop.
* Runs the non-harmonic Krylov-Schur loop.
* - Runs an Arnoldi step to generate the Rayleigh quotient and Krylov basis.
* - Schur decompose the Rayleigh quotient.
* - Permutes the Rayleigh quotient according to the eigenvalues.
* - Truncate the Krylov-Schur expansion.
*/
void operator()(const Field& v0, int _maxIter, int _Nm, int _Nk, int _Nstop, RealD *_shift=NULL, bool doubleOrthog = true) {
// RealD shift_=1.;
// shift = &shift_;
if(_shift) shift = _shift;
void operator()(const Field& v0, int _maxIter, int _Nm, int _Nk, int _Nstop, bool doubleOrthog = true) {
MaxIter = _maxIter;
Nm = _Nm; Nk = _Nk;
@@ -380,14 +375,10 @@ class KrylovSchur {
RealD approxLambdaMax = approxMaxEval(v0);
rtol = Tolerance * approxLambdaMax;
std::cout << GridLogMessage << "Approximate max eigenvalue: " << approxLambdaMax << std::endl;
// rtol = Tolerance;
b = Eigen::VectorXcd::Zero(Nm); // start as e_{k+1}
b(Nm-1) = 1.0;
// basis = new std::vector<Field> (Nm, Grid);
// evecs.reserve();
int start = 0;
Field startVec = v0;
littleEvecs = Eigen::MatrixXcd::Zero(Nm, Nm);
@@ -396,123 +387,65 @@ class KrylovSchur {
// Perform Arnoldi steps to compute Krylov basis and Rayleigh quotient (Hess)
arnoldiIteration(startVec, Nm, start, doubleOrthog);
startVec = u; // original code
startVec = u;
start = Nk;
std::cout << GridLogDebug << "b after Arnoldi " << b << std::endl;
// checkKSDecomposition();
RealD gamma;
Field uhat(Grid);
Eigen::MatrixXcd Btilde;
std::vector<Field> basis2_s;
Eigen::VectorXcd b_s;
#if 1
if (shift){
if(0){
Field w(Grid);
ComplexD coeff,coeff2;
for (int j = 0; j < Nm; j++) {
Linop.Op(basis[j], w);
for (int k = 0; k < Nm; k++) {
coeff2 = innerProduct(basis[k], basis[j]);
coeff = innerProduct(basis[k], w); // coeff = h_{ij}. Note that since {vi} is ONB it's OK to subtract it off after.
std::cout << GridLogMessage << " Rayleigh "<<k<<" "<<j<<" "<<Rayleigh (k,j)<<" "<<coeff << " <k|j> = " << coeff2 << std::endl;
}
coeff = innerProduct(basis[j], u); // coeff = h_{ij}. Note that since {vi} is ONB it's OK to subtract it off after.
std::cout << GridLogMessage << " u "<<j<<" "<<coeff << std::endl;
}
}
Eigen::MatrixXcd temp = Rayleigh;
for (int m=0;m<Nm;m++) temp(m,m) -= *shift;
Eigen::MatrixXcd RayleighS = temp.inverse(); // (B-tI)^-1
Eigen::MatrixXcd temp2;
// temp2 = RayleighS*temp;
// std::cout << GridLogDebug << "Shift inverse check: shift= "<<*shift<<" "<< temp2 <<std::endl;
temp2=RayleighS.adjoint(); //(B-tI)^-1*
Eigen::VectorXcd g = temp2*b; //g = (B-tI)^-1* * b
Btilde= Rayleigh + g*(b.adjoint());
Field utilde(Grid);
utilde = u;
for (int j = 0; j<Nm; j++){
utilde -= basis[j]*g(j);
}
ComplexSchurDecomposition schurS (Btilde, false, ritzFilter);
std::cout << GridLogMessage << "Shifted Schur eigenvalues shift = "<<*shift << std::endl;
schurS.schurReorder(Nk);
Eigen::MatrixXcd Q_s = schurS.getMatrixQ();
Eigen::MatrixXcd Qt_s = Q_s.adjoint(); // TODO should Q be real?
Eigen::MatrixXcd S_s = schurS.getMatrixS();
Btilde=schurS.getMatrixS();
b_s= b;
b_s=Q_s*b; // Q is Qt in SlepC, b_s=bhat
std::cout << GridLogMessage << " constructUR "<< std::endl;
constructUR(basis2_s, basis, Qt_s, Nm,Nk);
std::cout << GridLogMessage << " constructUR "<< std::endl;
Eigen::MatrixXcd RayTmp_s = Btilde(Eigen::seqN(0, Nk), Eigen::seqN(0, Nk));
Btilde = RayTmp_s;
std::vector<Field> basisTmp_s = std::vector<Field> (basis2_s.begin(), basis2_s.begin() + Nk);
basis2_s = basisTmp_s;
Eigen::VectorXcd btmp_s = b_s.head(Nk);
b_s = btmp_s;
Eigen::VectorXcd ghat = g;
ghat = -Q_s * g;
Eigen::VectorXcd gtmp_s = ghat.head(Nk);
ghat = gtmp_s;
uhat = utilde;
for (int j = 0; j<Nk; j++){
uhat -= basis2_s[j]*ghat(j);
}
gamma = std::sqrt(norm2(uhat));
uhat *= 1.0/gamma;
std::cout << GridLogMessage << " gamma "<<gamma << std::endl;
Btilde += ghat*(b_s.adjoint());
b_s *=gamma;
// Eq.(44)
if(0){
Field w(Grid);
ComplexD coeff,coeff2;
for (int j = 0; j < Nk; j++) {
Linop.Op(basis2_s[j], w);
for (int k = 0; k < Nk; k++) {
coeff2 = innerProduct(basis2_s[k], basis2_s[j]);
coeff = innerProduct(basis2_s[k], w); // coeff = h_{ij}. Note that since {vi} is ONB it's OK to subtract it off after.
std::cout << GridLogMessage << " Btilde "<<k<<" "<<j<<" "<<Btilde(k,j)<<" "<<coeff << " <k|j> = " << coeff2 << std::endl;
}
coeff = innerProduct(basis2_s[j], uhat); // coeff = h_{ij}. Note that since {vi} is ONB it's OK to subtract it off after.
coeff2 = innerProduct(uhat,w);
std::cout << GridLogMessage << " uhat "<<j<<" "<<coeff << " w "<< coeff2 << " b " << b_s (j) << " ghat "<<ghat(j)<< std::endl;
nonHarmonicRestart();
if (checkConvergedAndReport(i)) return;
}
}
}
#endif
/**
* Runs the harmonic (shifted) Krylov-Schur loop: extracts Ritz values of a
* shift-augmented Rayleigh quotient so that eigenvalues near `*_shift` are
* reordered to the top instead of the extremal ones.
*/
void operator()(const Field& v0, int _maxIter, int _Nm, int _Nk, int _Nstop, RealD *_shift, bool doubleOrthog = true) {
if (!shift){
assert(_shift && "harmonic KrylovSchur: shift must be non-null");
RealD shiftVal = *_shift;
MaxIter = _maxIter;
Nm = _Nm; Nk = _Nk;
Nstop = _Nstop;
ssq = norm2(v0);
RealD approxLambdaMax = approxMaxEval(v0);
rtol = Tolerance * approxLambdaMax;
std::cout << GridLogMessage << "Approximate max eigenvalue: " << approxLambdaMax << std::endl;
b = Eigen::VectorXcd::Zero(Nm); // start as e_{k+1}
b(Nm-1) = 1.0;
int start = 0;
Field startVec = v0;
littleEvecs = Eigen::MatrixXcd::Zero(Nm, Nm);
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;
start = Nk;
std::cout << GridLogDebug << "b after Arnoldi " << b << std::endl;
harmonicRestart(shiftVal);
if (checkConvergedAndReport(i)) return;
}
}
private:
/**
* Non-harmonic restart step: Schur-decompose Rayleigh, reorder by ritzFilter,
* rotate the basis into the Schur vectors, and truncate to the leading Nk.
*/
void nonHarmonicRestart() {
// Perform a Schur decomposition on Rayleigh
ComplexSchurDecomposition schur (Rayleigh, false, ritzFilter);
std::cout << GridLogDebug << "Schur decomp holds? " << schur.checkDecomposition() << std::endl;
@@ -524,8 +457,6 @@ if (!shift){
Eigen::MatrixXcd Q = schur.getMatrixQ();
Qt = Q.adjoint(); // TODO should Q be real?
Eigen::MatrixXcd S = schur.getMatrixS();
// std::cout << GridLogMessage << "Schur decomp holds after reorder? " << schur.checkDecomposition() << std::endl;
std::cout << GridLogMessage << "*** ROTATING TO SCHUR BASIS *** " << std::endl;
@@ -534,35 +465,16 @@ if (!shift){
b = Q * b; // b^\dag = b^\dag * Q^\dag <==> b = Q*b
std::vector<Field> basis2;
constructUR(basis2, basis, Qt, Nm,Nm);
basis = basis2;
if(0){
Field w(Grid);
ComplexD coeff,coeff2;
for (int j = 0; j < Nm; j++) {
Linop.Op(basis[j], w);
for (int k = 0; k < Nm; k++) {
coeff2 = innerProduct(basis[k], basis[j]);
coeff = innerProduct(basis[k], w); // coeff = h_{ij}. Note that since {vi} is ONB it's OK to subtract it off after.
std::cout << GridLogMessage << " Stilde "<<k<<" "<<j<<" "<<Rayleigh(k,j)<<" "<<coeff << " <k|j> = " << coeff2 << std::endl;
}
coeff = innerProduct(basis[j], u); // coeff = h_{ij}. Note that since {vi} is ONB it's OK to subtract it off after.
std::cout << GridLogMessage << " u"<<j<<" "<<coeff << std::endl;
}
}
}
constructUR(basis2, basis, Qt, Nm,Nk);
// basis = basis2;
std::cout << GridLogMessage << "*** TRUNCATING FOR RESTART *** " << std::endl;
if (!shift){
std::cout << GridLogDebug << "Rayleigh before truncation: " << std::endl << Rayleigh << std::endl;
Eigen::MatrixXcd RayTmp = Rayleigh(Eigen::seqN(0, Nk), Eigen::seqN(0, Nk));
Rayleigh = RayTmp;
std::vector<Field> basisTmp = std::vector<Field> (basis.begin(), basis.begin() + Nk);
std::vector<Field> basisTmp = std::vector<Field> (basis2.begin(), basis2.begin() + Nk);
basis = basisTmp;
Eigen::VectorXcd btmp = b.head(Nk);
@@ -570,32 +482,93 @@ if (!shift){
std::cout << GridLogDebug << "Rayleigh after truncation: " << std::endl << Rayleigh << std::endl;
checkKSDecomposition();
// Compute eigensystem of Rayleigh. Note the eigenvectors correspond to the sorted eigenvalues.
computeEigensystem(Rayleigh);
std::cout << GridLogMessage << "Eigenvalues (first Nk sorted): " << std::endl << evals << std::endl;
}
}
/**
* Harmonic restart step: Schur-decompose the shift-augmented Rayleigh quotient
* so Ritz values close to `shiftVal` are reordered to the top, then rotate and
* truncate exactly as in the non-harmonic case.
*/
void harmonicRestart(RealD shiftVal) {
Eigen::MatrixXcd temp = Rayleigh;
for (int m=0;m<Nm;m++) temp(m,m) -= shiftVal;
Eigen::MatrixXcd RayleighS = temp.inverse(); // (B-tI)^-1
Eigen::MatrixXcd temp2 = RayleighS.adjoint(); //(B-tI)^-1*
Eigen::VectorXcd g = temp2*b; //g = (B-tI)^-1* * b
Eigen::MatrixXcd Btilde = Rayleigh + g*(b.adjoint());
Field utilde(Grid);
utilde = u;
for (int j = 0; j<Nm; j++){
utilde -= basis[j]*g(j);
}
ComplexSchurDecomposition schurS (Btilde, false, ritzFilter);
std::cout << GridLogMessage << "Shifted Schur eigenvalues shift = "<<shiftVal << std::endl;
schurS.schurReorder(Nk);
Eigen::MatrixXcd Q_s = schurS.getMatrixQ();
Eigen::MatrixXcd Qt_s = Q_s.adjoint(); // TODO should Q be real?
Btilde=schurS.getMatrixS();
Eigen::VectorXcd b_s = Q_s*b; // Q is Qt in SlepC, b_s=bhat
std::vector<Field> basis2_s;
constructUR(basis2_s, basis, Qt_s, Nm,Nk);
Eigen::MatrixXcd RayTmp_s = Btilde(Eigen::seqN(0, Nk), Eigen::seqN(0, Nk));
Btilde = RayTmp_s;
std::vector<Field> basisTmp_s = std::vector<Field> (basis2_s.begin(), basis2_s.begin() + Nk);
basis2_s = basisTmp_s;
Eigen::VectorXcd btmp_s = b_s.head(Nk);
b_s = btmp_s;
Eigen::VectorXcd ghat = -Q_s * g;
Eigen::VectorXcd gtmp_s = ghat.head(Nk);
ghat = gtmp_s;
Field uhat(Grid);
uhat = utilde;
for (int j = 0; j<Nk; j++){
uhat -= basis2_s[j]*ghat(j);
}
RealD gamma = std::sqrt(norm2(uhat));
uhat *= 1.0/gamma;
std::cout << GridLogMessage << " gamma "<<gamma << std::endl;
Btilde += ghat*(b_s.adjoint());
b_s *=gamma;
if(shift){
Rayleigh = Btilde;
basis= basis2_s;
b = b_s;
beta_k = gamma;
u= uhat;
checkKSDecomposition();
computeEigensystem(Rayleigh);
std::cout << GridLogMessage << "Eigenvalues (first Nk sorted): " << std::endl << evals << std::endl;
}
// check convergence and return if needed.
/**
* Shared post-restart convergence check. On convergence (or the final
* iteration) reports eigenvalues and optionally the explicit residual
* check. Returns true if operator() should return.
*/
bool checkConvergedAndReport(int i) {
int 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 "
<< i << "." << std::endl;
// basisRotate(evecs, Qt, 0, Nk, 0, Nk, Nm); // Think this might have been the issue
std::cout << GridLogMessage << "Eigenvalues: " << std::endl << evals << std::endl;
if (doEvalCheck) {
@@ -611,13 +584,12 @@ if (!shift){
<< " || A v - eval_est * v || = " << res << std::endl;
}
}
return true;
}
return false;
}
// writeEigensystem(path);
return;
}
}
}
public:
/**
* Constructs the Arnoldi basis for the Krylov space K_n(D, src). (TODO make private)