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/* Ergo, version 3.8.2, a program for linear scaling electronic structure
* calculations.
* Copyright (C) 2023 Elias Rudberg, Emanuel H. Rubensson, Pawel Salek,
* and Anastasia Kruchinina.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* Primary academic reference:
* Ergo: An open-source program for linear-scaling electronic structure
* calculations,
* Elias Rudberg, Emanuel H. Rubensson, Pawel Salek, and Anastasia
* Kruchinina,
* SoftwareX 7, 107 (2018),
* <http://dx.doi.org/10.1016/j.softx.2018.03.005>
*
* For further information about Ergo, see <http://www.ergoscf.org>.
*/
/** @file simple_lanczos.cc
@brief Simple implementation of the Lanczos method.
@author: Elias Rudberg <em>responsible</em>
*/
#include "../matrix/mat_gblas.h"
#include "simple_lanczos.h"
#include "output.h"
#include <cmath>
#include <cstring>
namespace simple_lanczos {
ergo_real simple_lanczos_get_vector_norm(int n, const ergo_real* v) {
ergo_real sqSum = 0;
for(int i = 0; i < n; i++)
sqSum += v[i] * v[i];
return template_blas_sqrt(sqSum);
}
void simple_lanczos_normalize_vector(int n, ergo_real* v) {
ergo_real factor = 1.0 / simple_lanczos_get_vector_norm(n, v);
for(int i = 0; i < n; i++)
v[i] *= factor;
}
void simple_lanczos_get_eigs(int n, ergo_real* M,
ergo_real & currEig_lo, ergo_real* bestVector_lo,
ergo_real & currEig_hi, ergo_real* bestVector_hi,
ergo_real* eigValListResult)
{
int lwork = 3*n*n;
ergo_real* work = new ergo_real[lwork];
ergo_real* eigvalList = new ergo_real[n];
ergo_real* A = new ergo_real[n*n];
memcpy(A, M, n*n*sizeof(ergo_real));
int info = 0;
mat::syev("V", "U", &n, A,
&n, eigvalList, work, &lwork,
&info);
if(info != 0)
{
do_output(LOG_CAT_ERROR, LOG_AREA_CI, "error in syev, info = %i", info);
throw("error in syev");
}
if(bestVector_lo) {
for(int i = 0; i < n; i++)
bestVector_lo[i] = A[0*n+i];
}
if(bestVector_hi) {
for(int i = 0; i < n; i++)
bestVector_hi[i] = A[(n-1)*n+i];
}
if(eigValListResult)
{
for(int i = 0; i < n; i++)
eigValListResult[i] = eigvalList[i];
}
currEig_lo = eigvalList[0];
currEig_hi = eigvalList[n-1];
delete [] work;
delete [] eigvalList;
delete [] A;
}
} // end namespace simple_lanczos
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