template<typename MatrixType> void selfadjointeigensolver_essential_check(const MatrixType& m)
{
  typedef typename MatrixType::Scalar Scalar;
  typedef typename NumTraits<Scalar>::Real RealScalar;
  RealScalar eival_eps = (std::min)(test_precision<RealScalar>(),  NumTraits<Scalar>::dummy_precision()*20000);
  
  SelfAdjointEigenSolver<MatrixType> eiSymm(m);
  VERIFY_IS_EQUAL(eiSymm.info(), Success);
  VERIFY_IS_APPROX(m.template selfadjointView<Lower>() * eiSymm.eigenvectors(),
                   eiSymm.eigenvectors() * eiSymm.eigenvalues().asDiagonal());
  VERIFY_IS_APPROX(m.template selfadjointView<Lower>().eigenvalues(), eiSymm.eigenvalues());
  VERIFY_IS_UNITARY(eiSymm.eigenvectors());

  if(m.cols()<=4)
  {
    SelfAdjointEigenSolver<MatrixType> eiDirect;
    eiDirect.computeDirect(m);  
    VERIFY_IS_EQUAL(eiDirect.info(), Success);
    VERIFY_IS_APPROX(eiSymm.eigenvalues(), eiDirect.eigenvalues());
    if(! eiSymm.eigenvalues().isApprox(eiDirect.eigenvalues(), eival_eps) )
    {
      std::cerr << "reference eigenvalues: " << eiSymm.eigenvalues().transpose() << "\n"
                << "obtained eigenvalues:  " << eiDirect.eigenvalues().transpose() << "\n"
                << "diff:                  " << (eiSymm.eigenvalues()-eiDirect.eigenvalues()).transpose() << "\n"
                << "error (eps):           " << (eiSymm.eigenvalues()-eiDirect.eigenvalues()).norm() / eiSymm.eigenvalues().norm() << "  (" << eival_eps << ")\n";
    }
    VERIFY(eiSymm.eigenvalues().isApprox(eiDirect.eigenvalues(), eival_eps));
    VERIFY_IS_APPROX(m.template selfadjointView<Lower>() * eiDirect.eigenvectors(),
                    eiDirect.eigenvectors() * eiDirect.eigenvalues().asDiagonal());
    VERIFY_IS_APPROX(m.template selfadjointView<Lower>().eigenvalues(), eiDirect.eigenvalues());
    VERIFY_IS_UNITARY(eiDirect.eigenvectors());
  }
}
template<typename MatrixType> void selfadjointeigensolver(const MatrixType& m)
{
  typedef typename MatrixType::Index Index;
  /* this test covers the following files:
     EigenSolver.h, SelfAdjointEigenSolver.h (and indirectly: Tridiagonalization.h)
  */
  Index rows = m.rows();
  Index cols = m.cols();

  typedef typename MatrixType::Scalar Scalar;
  typedef typename NumTraits<Scalar>::Real RealScalar;

  RealScalar largerEps = 10*test_precision<RealScalar>();

  MatrixType a = MatrixType::Random(rows,cols);
  MatrixType a1 = MatrixType::Random(rows,cols);
  MatrixType symmA =  a.adjoint() * a + a1.adjoint() * a1;
  MatrixType symmC = symmA;

  // randomly nullify some rows/columns
  {
    Index count = 1;//internal::random<Index>(-cols,cols);
    for(Index k=0; k<count; ++k)
    {
      Index i = internal::random<Index>(0,cols-1);
      symmA.row(i).setZero();
      symmA.col(i).setZero();
    }
  }

  symmA.template triangularView<StrictlyUpper>().setZero();
  symmC.template triangularView<StrictlyUpper>().setZero();

  MatrixType b = MatrixType::Random(rows,cols);
  MatrixType b1 = MatrixType::Random(rows,cols);
  MatrixType symmB = b.adjoint() * b + b1.adjoint() * b1;
  symmB.template triangularView<StrictlyUpper>().setZero();

  SelfAdjointEigenSolver<MatrixType> eiSymm(symmA);
  SelfAdjointEigenSolver<MatrixType> eiDirect;
  eiDirect.computeDirect(symmA);
  // generalized eigen pb
  GeneralizedSelfAdjointEigenSolver<MatrixType> eiSymmGen(symmC, symmB);

  VERIFY_IS_EQUAL(eiSymm.info(), Success);
  VERIFY((symmA.template selfadjointView<Lower>() * eiSymm.eigenvectors()).isApprox(
          eiSymm.eigenvectors() * eiSymm.eigenvalues().asDiagonal(), largerEps));
  VERIFY_IS_APPROX(symmA.template selfadjointView<Lower>().eigenvalues(), eiSymm.eigenvalues());

  VERIFY_IS_EQUAL(eiDirect.info(), Success);
  VERIFY((symmA.template selfadjointView<Lower>() * eiDirect.eigenvectors()).isApprox(
          eiDirect.eigenvectors() * eiDirect.eigenvalues().asDiagonal(), largerEps));
  VERIFY_IS_APPROX(symmA.template selfadjointView<Lower>().eigenvalues(), eiDirect.eigenvalues());

  SelfAdjointEigenSolver<MatrixType> eiSymmNoEivecs(symmA, false);
  VERIFY_IS_EQUAL(eiSymmNoEivecs.info(), Success);
  VERIFY_IS_APPROX(eiSymm.eigenvalues(), eiSymmNoEivecs.eigenvalues());

  // generalized eigen problem Ax = lBx
  eiSymmGen.compute(symmC, symmB,Ax_lBx);
  VERIFY_IS_EQUAL(eiSymmGen.info(), Success);
  VERIFY((symmC.template selfadjointView<Lower>() * eiSymmGen.eigenvectors()).isApprox(
          symmB.template selfadjointView<Lower>() * (eiSymmGen.eigenvectors() * eiSymmGen.eigenvalues().asDiagonal()), largerEps));

  // generalized eigen problem BAx = lx
  eiSymmGen.compute(symmC, symmB,BAx_lx);
  VERIFY_IS_EQUAL(eiSymmGen.info(), Success);
  VERIFY((symmB.template selfadjointView<Lower>() * (symmC.template selfadjointView<Lower>() * eiSymmGen.eigenvectors())).isApprox(
         (eiSymmGen.eigenvectors() * eiSymmGen.eigenvalues().asDiagonal()), largerEps));

  // generalized eigen problem ABx = lx
  eiSymmGen.compute(symmC, symmB,ABx_lx);
  VERIFY_IS_EQUAL(eiSymmGen.info(), Success);
  VERIFY((symmC.template selfadjointView<Lower>() * (symmB.template selfadjointView<Lower>() * eiSymmGen.eigenvectors())).isApprox(
         (eiSymmGen.eigenvectors() * eiSymmGen.eigenvalues().asDiagonal()), largerEps));


  eiSymm.compute(symmC);
  MatrixType sqrtSymmA = eiSymm.operatorSqrt();
  VERIFY_IS_APPROX(MatrixType(symmC.template selfadjointView<Lower>()), sqrtSymmA*sqrtSymmA);
  VERIFY_IS_APPROX(sqrtSymmA, symmC.template selfadjointView<Lower>()*eiSymm.operatorInverseSqrt());

  MatrixType id = MatrixType::Identity(rows, cols);
  VERIFY_IS_APPROX(id.template selfadjointView<Lower>().operatorNorm(), RealScalar(1));

  SelfAdjointEigenSolver<MatrixType> eiSymmUninitialized;
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.info());
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.eigenvalues());
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.eigenvectors());
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.operatorSqrt());
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.operatorInverseSqrt());

  eiSymmUninitialized.compute(symmA, false);
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.eigenvectors());
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.operatorSqrt());
  VERIFY_RAISES_ASSERT(eiSymmUninitialized.operatorInverseSqrt());

  // test Tridiagonalization's methods
  Tridiagonalization<MatrixType> tridiag(symmC);
  // FIXME tridiag.matrixQ().adjoint() does not work
  VERIFY_IS_APPROX(MatrixType(symmC.template selfadjointView<Lower>()), tridiag.matrixQ() * tridiag.matrixT().eval() * MatrixType(tridiag.matrixQ()).adjoint());

  if (rows > 1)
  {
    // Test matrix with NaN
    symmC(0,0) = std::numeric_limits<typename MatrixType::RealScalar>::quiet_NaN();
    SelfAdjointEigenSolver<MatrixType> eiSymmNaN(symmC);
    VERIFY_IS_EQUAL(eiSymmNaN.info(), NoConvergence);
  }
}