LinearInterpolation Class Reference

This class interpolates values given a set of data pairs and an abscissa. More...

#include <LinearInterpolation.h>

Public Member Functions
	LinearInterpolation (const std::vector< Real > &X, const std::vector< Real > &Y)
	LinearInterpolation ()
virtual	~LinearInterpolation ()=default
void	setData (const std::vector< Real > &X, const std::vector< Real > &Y)
	Set the x and y values. More...
void	errorCheck ()
Real	sample (Real x) const
	This function will take an independent variable input and will return the dependent variable based on the generated fit. More...
Real	sampleDerivative (Real x) const
	This function will take an independent variable input and will return the derivative of the dependent variable with respect to the independent variable based on the generated fit. More...
void	dumpSampleFile (std::string base_name, std::string x_label="X", std::string y_label="Y", Real xmin=0, Real xmax=0, Real ymin=0, Real ymax=0)
	This function will dump GNUPLOT input files that can be run to show the data points and function fits. More...
unsigned int	getSampleSize ()
	This function returns the size of the array holding the points, i.e. More...
Real	integrate ()
	This function returns the integral of the function. More...
Real	domain (int i) const
Real	range (int i) const

Private Attributes
std::vector< Real >	_x
std::vector< Real >	_y

Static Private Attributes
static int	_file_number = 0

Detailed Description

This class interpolates values given a set of data pairs and an abscissa.

Definition at line 21 of file LinearInterpolation.h.

Constructor & Destructor Documentation

LinearInterpolation() [1/2]

LinearInterpolation::LinearInterpolation	(	const std::vector< Real > &	X,
		const std::vector< Real > &	Y
	)

Definition at line 18 of file LinearInterpolation.C.

  : _x(x), _y(y)
{
  errorCheck();
}

LinearInterpolation() [2/2]

LinearInterpolation::LinearInterpolation ( )

inline

Definition at line 29 of file LinearInterpolation.h.

: _x(std::vector<Real>()), _y(std::vector<Real>()) {}

~LinearInterpolation()

virtual LinearInterpolation::~LinearInterpolation ( )

virtualdefault

Member Function Documentation

domain()

Real LinearInterpolation::domain

(

int

i

)

const

Definition at line 89 of file LinearInterpolation.C.

{
  return _x[i];
}

dumpSampleFile()

void LinearInterpolation::dumpSampleFile	(	std::string	base_name,
		std::string	x_label = "X",
		std::string	y_label = "Y",
		Real	xmin = 0,
		Real	xmax = 0,
		Real	ymin = 0,
		Real	ymax = 0
	)

This function will dump GNUPLOT input files that can be run to show the data points and function fits.

Definition at line 101 of file LinearInterpolation.C.

{
  std::stringstream filename, filename_pts;
  const unsigned char fill_character = '0';
  const unsigned int field_width = 4;

  filename.fill(fill_character);
  filename << base_name;
  filename.width(field_width);
  filename << _file_number << ".plt";

  filename_pts.fill(fill_character);
  filename_pts << base_name << "_pts";
  filename_pts.width(field_width);
  filename_pts << _file_number << ".dat";

  /* First dump the GNUPLOT file with the Piecewise Linear Equations */
  std::ofstream out(filename.str().c_str());
  out.precision(15);
  out.fill(fill_character);

  out << "set terminal postscript color enhanced\n"
      << "set output \"" << base_name;
  out.width(field_width);
  out << _file_number << ".eps\"\n"
      << "set xlabel \"" << x_label << "\"\n"
      << "set ylabel \"" << y_label << "\"\n";
  if (xmin != 0 && xmax != 0)
    out << "set xrange [" << xmin << ":" << xmax << "]\n";
  if (ymin != 0 && ymax != 0)
    out << "set yrange [" << ymin << ":" << ymax << "]\n";
  out << "set key left top\n"
      << "f(x)=";

  for (unsigned int i = 1; i < _x.size(); ++i)
  {
    Real m = (_y[i] - _y[i - 1]) / (_x[i] - _x[i - 1]);
    Real b = (_y[i] - m * _x[i]);

    out << _x[i - 1] << "<=x && x<" << _x[i] << " ? " << m << "*x+(" << b << ") : ";
  }
  out << " 1/0\n";

  out << "\nplot f(x) with lines, '" << filename_pts.str() << "' using 1:2 title \"Points\"\n";
  out.close();

  assert(_x.size() == _y.size());

  out.open(filename_pts.str().c_str());
  /* Next dump the data points into a separate file */
  for (unsigned int i = 0; i < _x.size(); ++i)
    out << _x[i] << " " << _y[i] << "\n";
  out << std::endl;

  ++_file_number;
  out.close();
}

errorCheck()

void LinearInterpolation::errorCheck

(

)

Definition at line 25 of file LinearInterpolation.C.

Referenced by LinearInterpolation(), and setData().

{
  if (_x.size() != _y.size())
    throw std::domain_error("Vectors are not the same length");

  for (unsigned int i = 0; i + 1 < _x.size(); ++i)
    if (_x[i] >= _x[i + 1])
    {
      std::ostringstream oss;
      oss << "x-values are not strictly increasing: x[" << i << "]: " << _x[i] << " x[" << i + 1
          << "]: " << _x[i + 1];
      throw std::domain_error(oss.str());
    }
}

getSampleSize()

unsigned int LinearInterpolation::getSampleSize

(

)

This function returns the size of the array holding the points, i.e.

the number of sample points

Definition at line 166 of file LinearInterpolation.C.

{
  return _x.size();
}

integrate()

Real LinearInterpolation::integrate

(

)

This function returns the integral of the function.

Definition at line 79 of file LinearInterpolation.C.

{
  Real answer = 0;
  for (unsigned int i = 1; i < _x.size(); ++i)
    answer += 0.5 * (_y[i] + _y[i - 1]) * (_x[i] - _x[i - 1]);

  return answer;
}

range()

Real LinearInterpolation::range

(

int

i

)

const

Definition at line 95 of file LinearInterpolation.C.

{
  return _y[i];
}

sample()

Real LinearInterpolation::sample

(

Real

x

)

const

This function will take an independent variable input and will return the dependent variable based on the generated fit.

Definition at line 41 of file LinearInterpolation.C.

Referenced by IterationAdaptiveDT::computeDT(), and IterationAdaptiveDT::computeInterpolationDT().

{
  // sanity check (empty LinearInterpolations get constructed in many places
  // so we cannot put this into the errorCheck)
  assert(_x.size() > 0);

  // endpoint cases
  if (x <= _x[0])
    return _y[0];
  if (x >= _x.back())
    return _y.back();

  for (unsigned int i = 0; i + 1 < _x.size(); ++i)
    if (x >= _x[i] && x < _x[i + 1])
      return _y[i] + (_y[i + 1] - _y[i]) * (x - _x[i]) / (_x[i + 1] - _x[i]);

  throw std::out_of_range("Unreachable");
  return 0;
}

sampleDerivative()

Real LinearInterpolation::sampleDerivative

(

Real

x

)

const

This function will take an independent variable input and will return the derivative of the dependent variable with respect to the independent variable based on the generated fit.

Definition at line 62 of file LinearInterpolation.C.

{
  // endpoint cases
  if (x < _x[0])
    return 0.0;
  if (x >= _x[_x.size() - 1])
    return 0.0;

  for (unsigned int i = 0; i + 1 < _x.size(); ++i)
    if (x >= _x[i] && x < _x[i + 1])
      return (_y[i + 1] - _y[i]) / (_x[i + 1] - _x[i]);

  throw std::out_of_range("Unreachable");
  return 0;
}

setData()

void LinearInterpolation::setData ( const std::vector< Real > &  X, const std::vector< Real > &  Y  )

inline

Set the x and y values.

Definition at line 36 of file LinearInterpolation.h.

  {
    _x = X;
    _y = Y;
    errorCheck();
  }

Member Data Documentation

_file_number

int LinearInterpolation::_file_number = 0

staticprivate

Definition at line 88 of file LinearInterpolation.h.

Referenced by dumpSampleFile().

_x

std::vector<Real> LinearInterpolation::_x

private

Definition at line 85 of file LinearInterpolation.h.

Referenced by domain(), dumpSampleFile(), errorCheck(), getSampleSize(), integrate(), sample(), sampleDerivative(), and setData().

_y

std::vector<Real> LinearInterpolation::_y

private

Definition at line 86 of file LinearInterpolation.h.

Referenced by dumpSampleFile(), errorCheck(), integrate(), range(), sample(), sampleDerivative(), and setData().

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The documentation for this class was generated from the following files:

• include/utils/LinearInterpolation.h
• src/utils/LinearInterpolation.C