/*
* Copyright(C) 1999-2020, 2022, 2023 National Technology & Engineering Solutions
* of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with
* NTESS, the U.S. Government retains certain rights in this software.
*
* See packages/seacas/LICENSE for details
*/
#include "../main/defs.h"
#include "../main/structs.h"
#include "smalloc.h"
#include <math.h>
#include <stdio.h>
/* This is based on lanczos_SO but is simplified and tailored to solve
the extended eigen-problem using Rafael's technique. Solves Nx = lambda*Wx + Wg.
In the terminal propagation context we know that e^T Wg = 0 by virue of the way
g is constructed. This code, however, is designed to work in the more general
case of arbitrary g (but this capability has not been tested). Returns 0 if it
thinks everything's OK, nonzero otherwise. */
int lanczos_ext(struct vtx_data **A, /* sparse matrix in row linked list format */
int n, /* problem size */
int d, /* problem dimension = number of eigvecs to find */
double **y, /* columns of y are eigenvectors of A */
double eigtol, /* tolerance on eigenvectors */
double *vwsqrt, /* square roots of vertex weights */
double maxdeg, /* maximum degree of graph */
int version, /* flags which version of sel. orth. to use */
double *gvec, /* the rhs n-vector in the extended eigen problem */
double sigma /* specifies the norm constraint on extended
eigenvector */
)
{
extern FILE *Output_File; /* output file or null */
extern int LANCZOS_SO_INTERVAL; /* interval between orthogonalizations */
extern int LANCZOS_MAXITNS; /* maximum Lanczos iterations allowed */
extern int DEBUG_EVECS; /* print debugging output? */
extern int DEBUG_TRACE; /* trace main execution path */
extern int WARNING_EVECS; /* print warning messages? */
extern double BISECTION_SAFETY; /* safety for T bisection algorithm */
extern double SRESTOL; /* resid tol for T evec comp */
extern double DOUBLE_EPSILON; /* machine precision */
extern double DOUBLE_MAX; /* largest double value */
extern double splarax_time; /* time matvec */
extern double orthog_time; /* time orthogonalization work */
extern double evec_time; /* time to generate eigenvectors */
extern double ql_time; /* time tridiagonal eigenvalue work */
extern double blas_time; /* time for blas. linear algebra */
extern double init_time; /* time to allocate, initialize variables */
extern double scan_time; /* time for scanning eval and bound lists */
extern double debug_time; /* time for (some of) debug computations */
extern double ritz_time; /* time to generate ritz vectors */
extern double pause_time; /* time to compute whether to pause */
int i, j, k; /* indices */
int maxj; /* maximum number of Lanczos iterations */
double *u, *r; /* Lanczos vectors */
double *alpha, *beta; /* the Lanczos scalars from each step */
double *ritz; /* copy of alpha for ql */
double *workj; /* work vector, e.g. copy of beta for ql */
double *workn; /* work vector, e.g. product Av for checkeig */
double *s; /* eigenvector of T */
double **q; /* columns of q are Lanczos basis vectors */
double *bj; /* beta(j)*(last el. of corr. eigvec s of T) */
double Sres; /* how well Tevec calculated eigvec s */
double Sres_max; /* Max value of Sres */
int inc_bis_safety; /* has Sres increased? */
double *Ares; /* how well Lanczos calc. eigpair lambda,y */
int *index; /* the Ritz index of an eigenpair */
struct orthlink **solist; /* vec. of structs with vecs. to orthog. against */
struct scanlink *scanlist; /* linked list of fields to do with min ritz vals */
struct scanlink *curlnk; /* for traversing the scanlist */
double bis_safety; /* real safety for T bisection algorithm */
int converged; /* has the iteration converged? */
double goodtol; /* error tolerance for a good Ritz vector */
int ngood; /* total number of good Ritz pairs at current step */
int maxngood; /* biggest val of ngood through current step */
int left_ngood; /* number of good Ritz pairs on left end */
int lastpause; /* Most recent step with good ritz vecs */
int nopauses; /* Have there been any pauses? */
int interval; /* number of steps between pauses */
double time; /* Current clock time */
int left_goodlim; /* number of ritz pairs checked on left end */
double Anorm; /* Norm estimate of the Laplacian matrix */
int pausemode; /* which Lanczos pausing criterion to use */
int pause; /* whether to pause */
int temp; /* used to prevent redundant index computations */
double *extvec; /* n-vector solving the extended A eigenproblem */
double *v; /* j-vector solving the extended T eigenproblem */
double extval = 0.0; /* computed extended eigenvalue (of both A and T) */
double *work1, *work2; /* work vectors */
double check; /* to check an orthogonality condition */
double numerical_zero; /* used for zero in presence of round-off */
int ritzval_flag; /* status flag for get_ritzvals() */
int memory_ok; /* TRUE until memory runs out */
if (DEBUG_TRACE > 0) {
printf("<Entering lanczos_ext>\n");
}
if (DEBUG_EVECS > 0) {
printf("Selective orthogonalization Lanczos for extended eigenproblem, matrix size = %d.\n", n);
}
/* Initialize time. */
time = lanc_seconds();
if (d != 1) {
bail("ERROR: Extended Lanczos only available for bisection.", 1);
/* ... something must be wrong upstream. */
}
if (n < d + 1) {
bail("ERROR: System too small for number of eigenvalues requested.", 1);
/* ... d+1 since don't use zero eigenvalue pair */
}
/* Allocate space. */
maxj = LANCZOS_MAXITNS;
u = mkvec(1, n);
r = mkvec(1, n);
workn = mkvec(1, n);
Ares = mkvec(0, d);
index = smalloc((d + 1) * sizeof(int));
alpha = mkvec(1, maxj);
beta = mkvec(0, maxj);
ritz = mkvec(1, maxj);
s = mkvec(1, maxj);
bj = mkvec(1, maxj);
workj = mkvec(0, maxj);
q = smalloc((maxj + 1) * sizeof(double *));
solist = smalloc((maxj + 1) * sizeof(struct orthlink *));
scanlist = mkscanlist(d);
extvec = mkvec(1, n);
v = mkvec(1, maxj);
work1 = mkvec(1, maxj);
work2 = mkvec(1, maxj);
/* Set some constants governing orthogonalization */
ngood = 0;
maxngood = 0;
Anorm = 2 * maxdeg; /* Gershgorin estimate for ||A|| */
goodtol = Anorm * sqrt(DOUBLE_EPSILON); /* Parlett & Scott's bound, p.224 */
interval = 2 + min(LANCZOS_SO_INTERVAL - 2, n / (2 * LANCZOS_SO_INTERVAL));
bis_safety = BISECTION_SAFETY;
numerical_zero = 1.0e-13;
if (DEBUG_EVECS > 0) {
printf(" maxdeg %g\n", maxdeg);
printf(" goodtol %g\n", goodtol);
printf(" interval %d\n", interval);
printf(" maxj %d\n", maxj);
}
/* Initialize space. */
cpvec(r, 1, n, gvec);
if (vwsqrt != NULL) {
scale_diag(r, 1, n, vwsqrt);
}
check = ch_norm(r, 1, n);
if (vwsqrt == NULL) {
orthog1(r, 1, n);
}
else {
orthogvec(r, 1, n, vwsqrt);
}
check = fabs(check - ch_norm(r, 1, n));
if (check > 10 * numerical_zero && WARNING_EVECS > 0) {
strout("WARNING: In terminal propagation, rhs should have no component in the");
printf(" nullspace of the Laplacian, so check val %g should be negligible.\n", check);
if (Output_File != NULL) {
fprintf(Output_File,
" nullspace of the Laplacian, so check val %g should be negligible.\n",
check);
}
}
beta[0] = ch_norm(r, 1, n);
q[0] = mkvec(1, n);
setvec(q[0], 1, n, 0.0);
setvec(bj, 1, maxj, DOUBLE_MAX);
if (beta[0] < numerical_zero) {
/* The rhs vector, Dg, of the transformed problem is numerically zero or is
in the null space of the Laplacian, so this is not a well posed extended
eigenproblem. Set maxj to zero to force a quick exit but still clean-up
memory and return(1) to indicate to eigensolve that it should call the
default eigensolver routine for the standard eigenproblem. */
maxj = 0;
}
/* Main Lanczos loop. */
j = 1;
lastpause = 0;
pausemode = 1;
left_ngood = 0;
left_goodlim = 0;
converged = FALSE;
Sres_max = 0.0;
inc_bis_safety = FALSE;
nopauses = TRUE;
memory_ok = TRUE;
init_time += lanc_seconds() - time;
while ((j <= maxj) && (!converged) && memory_ok) {
time = lanc_seconds();
/* Allocate next Lanczos vector. If fail, back up to last pause. */
q[j] = mkvec_ret(1, n);
if (q[j] == NULL) {
memory_ok = FALSE;
if (DEBUG_EVECS > 0 || WARNING_EVECS > 0) {
strout("WARNING: Lanczos_ext out of memory; computing best approximation available.\n");
}
if (nopauses) {
bail("ERROR: Sorry, can't salvage Lanczos_ext.", 1);
/* ... save yourselves, men. */
}
for (i = lastpause + 1; i <= j - 1; i++) {
frvec(q[i], 1);
}
j = lastpause;
}
/* Basic Lanczos iteration */
vecscale(q[j], 1, n, 1.0 / beta[j - 1], r);
blas_time += lanc_seconds() - time;
time = lanc_seconds();
splarax(u, A, n, q[j], vwsqrt, workn);
splarax_time += lanc_seconds() - time;
time = lanc_seconds();
update(r, 1, n, u, -beta[j - 1], q[j - 1]);
alpha[j] = dot(r, 1, n, q[j]);
update(r, 1, n, r, -alpha[j], q[j]);
blas_time += lanc_seconds() - time;
/* Selective orthogonalization */
time = lanc_seconds();
if (vwsqrt == NULL) {
orthog1(r, 1, n);
}
else {
orthogvec(r, 1, n, vwsqrt);
}
if ((j == (lastpause + 1)) || (j == (lastpause + 2))) {
sorthog(r, n, solist, ngood);
}
orthog_time += lanc_seconds() - time;
beta[j] = ch_norm(r, 1, n);
time = lanc_seconds();
pause = lanpause(j, lastpause, interval, q, n, &pausemode, version, beta[j]);
pause_time += lanc_seconds() - time;
if (pause) {
nopauses = FALSE;
lastpause = j;
/* Compute limits for checking Ritz pair convergence. */
if (version == 2) {
if (left_ngood + 2 > left_goodlim) {
left_goodlim = left_ngood + 2;
}
}
/* Special case: need at least d Ritz vals on left. */
left_goodlim = max(left_goodlim, d);
/* Special case: can't find more than j total Ritz vals. */
if (left_goodlim > j) {
left_goodlim = min(left_goodlim, j);
}
/* Find Ritz vals using faster of Sturm bisection or ql. */
time = lanc_seconds();
if (inc_bis_safety) {
bis_safety *= 10;
inc_bis_safety = FALSE;
}
ritzval_flag =
get_ritzvals(alpha, beta, j, Anorm, workj, ritz, d, left_goodlim, 0, eigtol, bis_safety);
ql_time += lanc_seconds() - time;
if (ritzval_flag != 0) {
bail("ERROR: Lanczos_ext failed in computing eigenvalues of T.", 1);
/* ... we recover from this in lanczos_SO, but don't worry here. */
}
/* Scan for minimum evals of tridiagonal. */
time = lanc_seconds();
scanmin(ritz, 1, j, &scanlist);
scan_time += lanc_seconds() - time;
/* Compute Ritz pair bounds at left end. */
time = lanc_seconds();
setvec(bj, 1, j, 0.0);
for (i = 1; i <= left_goodlim; i++) {
Sres = Tevec(alpha, beta - 1, j, ritz[i], s);
if (Sres > Sres_max) {
Sres_max = Sres;
}
if (Sres > SRESTOL) {
inc_bis_safety = TRUE;
}
bj[i] = s[j] * beta[j];
}
ritz_time += lanc_seconds() - time;
/* Show portion of spectrum checked for Ritz convergence. */
if (DEBUG_EVECS > 2) {
time = lanc_seconds();
printf("\nindex Ritz vals bji bounds\n");
for (i = 1; i <= left_goodlim; i++) {
printf(" %3d", i);
doubleout(ritz[i], 1);
doubleout(bj[i], 1);
printf("\n");
}
printf("\n");
curlnk = scanlist;
while (curlnk != NULL) {
temp = curlnk->indx;
if ((temp > left_goodlim) && (temp < j)) {
printf(" %3d", temp);
doubleout(ritz[temp], 1);
doubleout(bj[temp], 1);
printf("\n");
}
curlnk = curlnk->pntr;
}
printf(" -------------------\n");
printf(" goodtol: %19.16f\n\n", goodtol);
debug_time += lanc_seconds() - time;
}
get_extval(alpha, beta, j, ritz[1], s, eigtol, beta[0], sigma, &extval, v, work1, work2);
/* Check convergence of iteration. */
if (fabs(beta[j] * v[j]) < eigtol) {
converged = TRUE;
}
else {
converged = FALSE;
}
if (!converged) {
ngood = 0;
left_ngood = 0; /* for setting left_goodlim on next loop */
/* Compute converged Ritz pairs on left end */
time = lanc_seconds();
for (i = 1; i <= left_goodlim; i++) {
if (bj[i] <= goodtol) {
ngood += 1;
left_ngood += 1;
if (ngood > maxngood) {
maxngood = ngood;
solist[ngood] = makeorthlnk();
(solist[ngood])->vec = mkvec(1, n);
}
(solist[ngood])->index = i;
Sres = Tevec(alpha, beta - 1, j, ritz[i], s);
if (Sres > Sres_max) {
Sres_max = Sres;
}
if (Sres > SRESTOL) {
inc_bis_safety = TRUE;
}
setvec((solist[ngood])->vec, 1, n, 0.0);
for (k = 1; k <= j; k++) {
scadd((solist[ngood])->vec, 1, n, s[k], q[k]);
}
}
}
ritz_time += lanc_seconds() - time;
if (DEBUG_EVECS > 2) {
time = lanc_seconds();
/* Show some info on the orthogonalization. */
printf(" j %3d; goodlim lft %2d, rgt %2d; list ", j, left_goodlim, 0);
solistout(solist, ngood, j);
/* Assemble current approx. eigenvector, check residual directly. */
setvec(y[1], 1, n, 0.0);
for (k = 1; k <= j; k++) {
scadd(y[1], 1, n, v[k], q[k]);
}
printf(" extended eigenvalue %g\n", extval);
printf(" est. extended residual %g\n", fabs(v[j] * beta[j]));
checkeig_ext(workn, u, A, y[1], n, extval, vwsqrt, gvec, eigtol, FALSE);
printf("---------------------end of iteration---------------------\n\n");
debug_time += lanc_seconds() - time;
}
}
}
j++;
}
j--;
if (DEBUG_EVECS > 0) {
time = lanc_seconds();
if (maxj == 0) {
printf("Not extended eigenproblem -- calling ordinary eigensolver.\n");
}
else {
printf(" Lanczos_ext itns: %d\n", j);
printf(" extended eigenvalue: %g\n", extval);
if (j == maxj) {
strout("WARNING: Maximum number of Lanczos iterations reached.\n");
}
}
debug_time += lanc_seconds() - time;
}
if (maxj != 0) {
/* Compute (scaled) extended eigenvector. */
time = lanc_seconds();
setvec(y[1], 1, n, 0.0);
for (k = 1; k <= j; k++) {
scadd(y[1], 1, n, v[k], q[k]);
}
evec_time += lanc_seconds() - time;
/* Note: assign() will scale this y vector back to x (since y = Dx) */
/* Compute and check residual directly. */
if (DEBUG_EVECS > 0 || WARNING_EVECS > 0) {
time = lanc_seconds();
checkeig_ext(workn, u, A, y[1], n, extval, vwsqrt, gvec, eigtol, TRUE);
debug_time += lanc_seconds() - time;
}
}
/* free up memory */
time = lanc_seconds();
frvec(u, 1);
frvec(r, 1);
frvec(workn, 1);
frvec(Ares, 0);
sfree(index);
frvec(alpha, 1);
frvec(beta, 0);
frvec(ritz, 1);
frvec(s, 1);
frvec(bj, 1);
frvec(workj, 0);
for (i = 0; i <= j; i++) {
frvec(q[i], 1);
}
sfree(q);
while (scanlist != NULL) {
curlnk = scanlist->pntr;
sfree(scanlist);
scanlist = curlnk;
}
for (i = 1; i <= maxngood; i++) {
frvec((solist[i])->vec, 1);
sfree(solist[i]);
}
sfree(solist);
frvec(extvec, 1);
frvec(v, 1);
frvec(work1, 1);
frvec(work2, 1);
init_time += lanc_seconds() - time;
if (maxj == 0) {
return (1); /* see note on beta[0] and maxj above */
}
return (0);
}