/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  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.txt
 *
 *  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.
 *
 *=========================================================================*/
#ifndef itkElasticBodyReciprocalSplineKernelTransform_hxx
#define itkElasticBodyReciprocalSplineKernelTransform_hxx

namespace itk
{
template <typename TParametersValueType, unsigned int VDimension>
ElasticBodyReciprocalSplineKernelTransform<TParametersValueType,
                                           VDimension>::ElasticBodyReciprocalSplineKernelTransform()
{
  // Alpha = 8 ( 1 - \nu ) - 1
  m_Alpha = 8.0 * (1.0 - .25) - 1;
}

template <typename TParametersValueType, unsigned int VDimension>
void
ElasticBodyReciprocalSplineKernelTransform<TParametersValueType, VDimension>::ComputeG(const InputVectorType & x,
                                                                                       GMatrixType & gmatrix) const
{
  const TParametersValueType r = x.GetNorm();
  const TParametersValueType factor = (r > 1e-8) ? (-1.0 / r) : TParametersValueType{};
  const TParametersValueType radial = m_Alpha * r;

  for (unsigned int i = 0; i < VDimension; ++i)
  {
    const typename InputVectorType::ValueType xi = x[i] * factor;
    // G is symmetric
    for (unsigned int j = 0; j < i; ++j)
    {
      const TParametersValueType value = xi * x[j];
      gmatrix[i][j] = value;
      gmatrix[j][i] = value;
    }
    gmatrix[i][i] = radial + xi * x[i];
  }
}

template <typename TParametersValueType, unsigned int VDimension>
void
ElasticBodyReciprocalSplineKernelTransform<TParametersValueType, VDimension>::PrintSelf(std::ostream & os,
                                                                                        Indent         indent) const
{
  Superclass::PrintSelf(os, indent);

  os << indent << "Alpha: " << static_cast<typename NumericTraits<TParametersValueType>::PrintType>(m_Alpha)
     << std::endl;
}
} // namespace itk
#endif
