symtrieig.h

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#ifndef SYMTRIEIG_H
#define SYMTRIEIG_H

// routines for symmetric eigenvalue problems, invoking LAPACK routine sstev_ (single precision) or dstev_ (double precision)

#include <iostream>  // for ostream
#include "matkitdef.h"

#ifdef USE_NAMESPACE
using namespace MATKIT;
namespace MATKIT {
#endif

class Vector;
class Matrix;

#ifdef USE_NAMESPACE
}  // end of namespace MATKIT
#endif




// compute all eigenvalues (but not eigenvectors) of a symmetric tridiagonal matrix
// n is the dimension of the symmetric tridiagonal matrix
// diag[],sdiag[] define the symmetric tridiagonal matrix:
//     the diagonal elements are diag[0,...,n-1] in order and the subdiagonal elements are sdiag[0,...,n-2] in order
// eigVal is the output vector of length n containing all eigenvalues in ascending order
// the return value is the flag returned by the LAPACK routine dstev_() (if Real is double) or stev_() (if Real is float)
int SymmetricTridiagoanlEigenSolver(Vector &eigVal, mkIndex n, const Real *diag, const Real *sdiag);


// compute all eigenvalues and eigenvectors of a symmetric tridiagonal matrix
// n is the dimension of the symmatrix tridiagonal matrix
// diag[],sdiag[] define the symmetric tridiagonal matrix:
//     the diagonal elements are diag[0,...,n-1] in order and the subdiagonal elements are sdiag[0,...,n-2] in order
// eigVal is the output vector of length n containing all eigenvalues in ascending order
// eigVec is the output n-by-n matrix with columns as eigenvectors, in the order as elements in eigVal
// the return value is the flag returned by the LAPACK routine dstev_() (if Real is double) or stev_() (if Real is float)
int SymmetricTridiagoanlEigenSolver(Vector &eigVal, Matrix &eigVec, mkIndex n, const Real *diag, const Real *sdiag);


// print out an error message to std::ostream outerr if info!=0 which signifies an error that occurred in the LAPACK routine xSTEV
// outerr is an std::ostream for printing out the error message when info!=0
// info is the flag returned from the LAPACK routine dstev_() (if Real is double) or sstev_() (if Real is float)
// = 0:  successful exit  (nothing will be printed)
// < 0:  if info = -i, the i-th argument had an illegal value
// > 0:  if info = i, the algorithm failed to converge; i off-diagonal elements did not converge to zero
// n is the dimension of the symmetric tridiagonal matrix; this information will also be printed out if n is provided (i.e. n!=0)
void reportTroubleIfAny(std::ostream &outerr, int info, mkIndex n=0);
  // end of group_symtrieig


#endif