Function eigen_matrix_symmetric 

pub fn eigen_matrix_symmetric(
    a: &Matrix,
    which: &EigenWhich,
    algorithm: EigenAlgorithm,
    options: &ArpackOptions,
) -> Result<SymmetricEigen>

Selected eigenvalues and eigenvectors of a real symmetric dense matrix (igraph_eigen_matrix_symmetric), with LAPACK or ARPACK.

Only the upper triangle is used by LAPACK. options tunes ARPACK: only its tol and mxiter are used (which, nev and ncv are derived from which, and ARPACK starts from a random vector of the calling thread’s RNG). Matrices of order at most 2 always use LAPACK.

Binds igraph_eigen_matrix_symmetric (see the linear algebra chapter).

Errors

If the matrix is not square or empty, the choice is invalid for the matrix order, or not supported by the algorithm (e.g. Select with ARPACK gives ErrorKind::Unimplemented).

Examples

use igraph::{linalg::*, prelude::*};
// Eigenvalues of [[2, 1], [1, 2]] are 1 and 3.
let a = Matrix::from_rows(&[[2.0, 1.0], [1.0, 2.0]]).unwrap();
let e = eigen_matrix_symmetric(&a, &EigenWhich::All, EigenAlgorithm::Lapack, &ArpackOptions::default()).unwrap();
let mut values = e.values.clone();
values.sort_by(f64::total_cmp);
assert!((values[0] - 1.0).abs() < 1e-12 && (values[1] - 3.0).abs() < 1e-12);