part_grid_threshold_thickness.cc

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// Copyright (C) 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2021, 2022, 2023 PISM Authors
//
// This file is part of PISM.
//
// PISM is free software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the Free Software
// Foundation; either version 3 of the License, or (at your option) any later
// version.
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// FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
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#include <cmath>
 
#include "pism/geometry/part_grid_threshold_thickness.hh"
#include "pism/util/Mask.hh"
 
namespace pism {
 
 
//! \file part_grid_threshold_thickness.cc Methods implementing PIK option -part_grid [\ref Albrechtetal2011].
 
//! @brief Compute threshold thickness used when deciding if a
//! partially-filled cell should be considered 'full'.
double part_grid_threshold_thickness(stencils::Star<int> cell_type,
                                     stencils::Star<double> ice_thickness,
                                     stencils::Star<double> surface_elevation,
                                     double bed_elevation) {
  // get mean ice thickness and surface elevation over adjacent
  // icy cells
  double
    H_average   = 0.0,
    h_average   = 0.0,
    H_threshold = 0.0;
  int N = 0;
 
  for (auto d : {North, East, South, West}) {
    if (mask::icy(cell_type[d])) {
      H_average += ice_thickness[d];
      h_average += surface_elevation[d];
      N++;
    }
  }
 
  if (N == 0) {
    // If there are no "icy" neighbors, return the threshold thickness
    // of zero, forcing Href to be converted to ice_thickness immediately.
    return 0.0;
  }
 
  H_average = H_average / N;
  h_average = h_average / N;
 
  if (bed_elevation + H_average > h_average) {
    H_threshold = h_average - bed_elevation;
  } else {
    H_threshold = H_average;
  }
 
  // make sure that the returned threshold thickness is non-negative:
  return std::max(H_threshold, 0.0);
}
 
} // end of namespace pism