Interpolation.cpp

#include "MantidKernel/Interpolation.h"
#include "MantidKernel/Logger.h"
#include "MantidKernel/UnitFactory.h"
#include <MantidKernel/StringTokenizer.h>

#include <algorithm>
#include <iterator>
#include <stdexcept>

namespace Mantid {
namespace Kernel {
namespace {
/// static logger
Logger g_log("Interpolation");
}

/* Functor for findIndexOfNextLargerValue, used in std::lower_bound to replicate
   the original behavior.
*/
struct LessOrEqualFunctor {
  bool operator()(const double &lhs, const double &rhs) { return lhs <= rhs; }
};

/** Constructor default to linear interpolation and x-unit set to TOF
 */
Interpolation::Interpolation() : m_method("linear") {
  m_xUnit = UnitFactory::Instance().create("TOF");
  m_yUnit = UnitFactory::Instance().create("TOF");
}

size_t
Interpolation::findIndexOfNextLargerValue(const std::vector<double> &data,
                                          double key) const {
  auto begin = data.begin();
  auto end = data.end();
  auto pos = std::lower_bound(begin, end, key, LessOrEqualFunctor());

  if (pos == end || pos == begin) {
    throw std::range_error("Value is not in the interpolation range.");
  }

  return std::distance(begin, pos);
}

void Interpolation::setXUnit(const std::string &unit) {
  m_xUnit = UnitFactory::Instance().create(unit);
}

void Interpolation::setYUnit(const std::string &unit) {
  m_yUnit = UnitFactory::Instance().create(unit);
}

/** Get interpolated value at location at
* @param at :: Location where to get interpolated value
* @return the value
*/
double Interpolation::value(const double &at) const {
  size_t N = m_x.size();

  if (N == 0) {
    g_log.error() << "Need at least one value for interpolation. Return "
                     "interpolation value zero.";
    return 0.0;
  }

  if (N == 1) {
    return m_y[0];
  }

  // check first if at is within the limits of interpolation interval

  if (at < m_x[0]) {
    return m_y[0] - (m_x[0] - at) * (m_y[1] - m_y[0]) / (m_x[1] - m_x[0]);
  }

  if (at >= m_x[N - 1]) {
    return m_y[N - 1] +
           (at - m_x[N - 1]) * (m_y[N - 1] - m_y[N - 2]) /
               (m_x[N - 1] - m_x[N - 2]);
  }

  try {
    // otherwise
    // General case. Find index of next largest value by std::lower_bound.
    size_t idx = findIndexOfNextLargerValue(m_x, at);
    return m_y[idx - 1] +
           (at - m_x[idx - 1]) * (m_y[idx] - m_y[idx - 1]) /
               (m_x[idx] - m_x[idx - 1]);
  } catch (const std::range_error &) {
    return 0.0;
  }
}

/** Add point in the interpolation.
*
* @param xx :: x-value
* @param yy :: y-value
*/
void Interpolation::addPoint(const double &xx, const double &yy) {
  size_t N = m_x.size();
  std::vector<double>::iterator it;

  if (N == 0) {
    m_x.push_back(xx);
    m_y.push_back(yy);
    return;
  }

  // check first if xx is within the limits of interpolation interval

  if (xx <= m_x[0]) {
    it = m_x.begin();
    it = m_x.insert(it, xx);
    it = m_y.begin();
    it = m_y.insert(it, yy);
    return;
  }

  if (xx >= m_x[N - 1]) {
    m_x.push_back(xx);
    m_y.push_back(yy);
    return;
  }

  // otherwise

  for (unsigned int i = 1; i < N; i++) {
    if (m_x[i] > xx) {
      it = m_x.begin();
      it = m_x.insert(it + i, xx);
      it = m_y.begin();
      it = m_y.insert(it + i, yy);
      return;
    }
  }
}

/**
  Prints object to stream
  @param os :: the Stream to output to
*/
void Interpolation::printSelf(std::ostream &os) const {
  os << m_method << " ; " << m_xUnit->unitID() << " ; " << m_yUnit->unitID();

  for (unsigned int i = 0; i < m_x.size(); i++) {
    os << " ; " << m_x[i] << " " << m_y[i];
  }
}

/**
  Resets interpolation data by clearing the internal storage for x- and y-values
*/
void Interpolation::resetData() {
  m_x.clear();
  m_y.clear();
}

/**
  Prints the value of parameter
  @param os :: the Stream to output to
  @param f :: the FitParameter to output
  @return the output stream
  */
std::ostream &operator<<(std::ostream &os, const Interpolation &f) {
  f.printSelf(os);
  return os;
}

/**
  Reads in parameter value
  @param in :: Input Stream
  @param f :: FitParameter to write to
  @return Current state of stream
*/
std::istream &operator>>(std::istream &in, Interpolation &f) {

  using tokenizer = Mantid::Kernel::StringTokenizer;
  std::string str;
  getline(in, str);
  tokenizer values(str, ";", tokenizer::TOK_TRIM);

  f.setMethod(values[0]);
  f.setXUnit(values[1]);
  f.setYUnit(values[2]);
  f.resetData(); // Reset data, in case the interpolation table is not empty

  for (unsigned int i = 3; i < values.count(); i++) {
    std::stringstream str(values[i]);
    double x, y;

    str >> x >> y;

    f.addPoint(x, y);
  }

  return in;
}

} // namespace Kernel
} // namespace Mantid