LogarithmScale.cpp

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// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2018 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
//----------------------------------------------------------------------
// Includes
//----------------------------------------------------------------------
#include <cmath>
#include <stdexcept>
 
#include "MantidAPI/LogarithmScale.h"
#include "MantidAPI/TransformScaleFactory.h"
#include "MantidKernel/Logger.h"
 
namespace Mantid::API {
namespace {
Kernel::Logger g_log("LogarithmScale");
} // namespace
 
DECLARE_TRANSFORMSCALE(LogarithmScale)
 
void LogarithmScale::setBase(const double base) {
  if (base <= 0) {
    g_log.error("Error: logarithm base must be a positive number");
  }
  m_base = base;
}
 
/* Transform the grid to adopt a logarithm scale.
 * @param gd a grid object
 */
void LogarithmScale::transform(std::vector<double> &gd) {
  double a = 1.0 / log(m_base);
  size_t n = gd.size();
  if (n == 0)
    return; // no need to process
  if (gd.front() <= 0) {
    g_log.error("LogarithmScale::transform Error: negative values");
    return;
  }
  if (n < 3)
    return; // no need to process
  double startX = a * log(gd.front());
  double endX = a * log(gd.back());
  double spacing = (endX - startX) / double(n);
 
  double x = startX + spacing;
  for (auto it = gd.begin() + 1; it != gd.end() - 1; it++) {
    *it = pow(m_base, x);
    x += spacing;
  }
}
 
} // namespace Mantid::API