transformation.cpp

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// Copyright (c) 2010-2023, Lawrence Livermore National Security, LLC. Produced
// at the Lawrence Livermore National Laboratory. All Rights reserved. See files
// LICENSE and NOTICE for details. LLNL-CODE-806117.
//
// This file is part of the MFEM library. For more information and source code
// availability visit https://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the BSD-3 license. We welcome feedback and contributions, see file
// CONTRIBUTING.md for details

#include "transformation.hpp"
#include <cmath>
#include <functional>

namespace mfem
{
namespace spde
{

// ---------------------------------------------------------------------------
// Functions for TransformedCoefficient interface
// ---------------------------------------------------------------------------

/// This function effectively implements equation 19 of the paper (see header).
///  `\Phi [y(x)]`
double TransformToUniform(double x) { return std::erfc(-x / std::sqrt(2)) / 2; }

double ApplyLevelSetAtZero(double x) { return x >= 0 ? 1 : 0; }

// ---------------------------------------------------------------------------
// Member functions for GFTransformer class
// ---------------------------------------------------------------------------

void UniformGRFTransformer::Transform(ParGridFunction &x) const
{
   GridFunctionCoefficient gf_coeff(&x);
   ConstantCoefficient factor(max_ - min_);
   ConstantCoefficient summand(min_);
   TransformedCoefficient transformation_coeff(&gf_coeff, TransformToUniform);
   ProductCoefficient product_coeff(transformation_coeff, factor);
   SumCoefficient sum_coeff(product_coeff, summand);
   ParGridFunction xx(x);
   xx.ProjectCoefficient(sum_coeff);
   x = xx;
}

void OffsetTransformer::Transform(ParGridFunction &x) const
{
   ConstantCoefficient offset(offset_);
   ParGridFunction xx(x);
   xx.ProjectCoefficient(offset);
   x += xx;
}

void ScaleTransformer::Transform(ParGridFunction &x) const { x *= scale_; }

void LevelSetTransformer::Transform(ParGridFunction &x) const
{
   GridFunctionCoefficient gf_coeff(&x);
   ConstantCoefficient threshold(-threshold_);
   SumCoefficient sum_coeff(gf_coeff, threshold);
   TransformedCoefficient transformation_coeff(&sum_coeff, ApplyLevelSetAtZero);
   ParGridFunction xx(x);
   xx.ProjectCoefficient(transformation_coeff);
   x = xx;
}

}  // namespace spde
}  // namespace mfem