// SPDX-License-Identifier: Apache-2.0
// 
// Copyright 2008-2016 Conrad Sanderson (https://conradsanderson.id.au)
// Copyright 2008-2016 National ICT Australia (NICTA)
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// https://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ------------------------------------------------------------------------


//! \addtogroup fn_eig_sym
//! @{


//! Eigenvalues of real/complex symmetric/hermitian matrix X
template<typename T1>
inline
typename enable_if2< is_blas_type<typename T1::elem_type>::value, bool >::result
eig_sym
  (
         Col<typename T1::pod_type>&     eigval,
  const Base<typename T1::elem_type,T1>& X
  )
  {
  arma_debug_sigprint();
  
  typedef typename T1::elem_type eT;
  
  Mat<eT> A(X.get_ref());
  
  const bool status = auxlib::eig_sym(eigval, A);
  
  if(status == false)
    {
    eigval.soft_reset();
    arma_warn(3, "eig_sym(): decomposition failed");
    }
  
  return status;
  }



//! Eigenvalues of real/complex symmetric/hermitian matrix X
template<typename T1>
arma_warn_unused
inline
typename enable_if2< is_blas_type<typename T1::elem_type>::value, Col<typename T1::pod_type> >::result
eig_sym
  (
  const Base<typename T1::elem_type,T1>& X
  )
  {
  arma_debug_sigprint();
  
  typedef typename T1::elem_type eT;
  typedef typename T1::pod_type   T;
  
  Col< T> eigval;
  Mat<eT> A(X.get_ref());
  
  const bool status = auxlib::eig_sym(eigval, A);

  if(status == false)
    {
    eigval.reset();
    arma_stop_runtime_error("eig_sym(): decomposition failed");
    }
  
  return eigval;
  }



//! internal helper function
template<typename eT>
inline
bool
eig_sym_helper
  (
        Col<typename get_pod_type<eT>::result>& eigval,
        Mat<eT>&                                eigvec,
  const Mat<eT>&                                X,
  const char                                    method_sig,
  const char*                                   caller_sig
  )
  {
  arma_debug_sigprint();
  
  if((arma_config::check_conform) && (auxlib::rudimentary_sym_check(X) == false))
    {
    if(is_cx<eT>::no )  { arma_warn(1, caller_sig, ": given matrix is not symmetric"); }
    if(is_cx<eT>::yes)  { arma_warn(1, caller_sig, ": given matrix is not hermitian"); }
    }
  
  bool status = false;
  
  if(method_sig == 'd')
    {
    const bool allow_dc = (sizeof(blas_int) >= std::size_t(8)) ? true : (X.n_rows <= uword(32000));
    
    if(allow_dc)
      {
      status = auxlib::eig_sym_dc(eigval, eigvec, X);
      }
    else
      {
      arma_warn(3, caller_sig, ": matrix size too large for divide-and-conquer algorithm; using standard algorithm instead");
      }
    }
  
  if(status == false)
    {
    status = auxlib::eig_sym(eigval, eigvec, X);
    }
  
  return status;
  }



//! Eigenvalues and eigenvectors of real/complex symmetric/hermitian matrix X
template<typename T1> 
inline
typename enable_if2< is_blas_type<typename T1::elem_type>::value, bool >::result
eig_sym
  (
         Col<typename T1::pod_type>&     eigval,
         Mat<typename T1::elem_type>&    eigvec,
  const Base<typename T1::elem_type,T1>& expr,
  const char* method =                   "dc"
  )
  {
  arma_debug_sigprint();
  
  typedef typename T1::elem_type eT;
  
  const char sig = (method != nullptr) ? method[0] : char(0);
  
  arma_conform_check( ((sig != 's') && (sig != 'd')),         "eig_sym(): unknown method specified"                             );
  arma_conform_check( void_ptr(&eigval) == void_ptr(&eigvec), "eig_sym(): parameter 'eigval' is an alias of parameter 'eigvec'" );
  
  const quasi_unwrap<T1> U(expr.get_ref());
  
  const bool is_alias = U.is_alias(eigvec);
  
  Mat<eT>  eigvec_tmp;
  Mat<eT>& eigvec_out = (is_alias == false) ? eigvec : eigvec_tmp;
  
  const bool status = eig_sym_helper(eigval, eigvec_out, U.M, sig, "eig_sym()");
  
  if(status == false)
    {
    eigval.soft_reset();
    eigvec.soft_reset();
    arma_warn(3, "eig_sym(): decomposition failed");
    }
  else
    {
    if(is_alias)  { eigvec.steal_mem(eigvec_tmp); }
    }
  
  return status;
  }



//! @}
