smash::Tabulation Class Reference

#include <tabulation.h>

A class for storing a one-dimensional lookup table of floating-point values.

Definition at line 33 of file tabulation.h.

Collaboration diagram for smash::Tabulation:

Public Member Functions
	Tabulation (double x_min, double range, int num, std::function< double(double)> f)
	Construct a new tabulation object. More...
double	get_value_step (double x) const
	Look up a value from the tabulation (without any interpolation, simply using the closest tabulated value). More...
double	get_value_linear (double x, Extrapolation extrapolation=Extrapolation::Linear) const
	Look up a value from the tabulation using linear interpolation. More...

Protected Attributes
std::vector< double >	values_
	vector for storing tabulated values More...
const double	x_min_
	lower bound for tabulation More...
const double	x_max_
	upper bound for tabulation More...
const double	inv_dx_
	inverse step size 1/dx More...

Constructor & Destructor Documentation

Tabulation()

smash::Tabulation::Tabulation	(	double	x_min,
		double	range,
		int	num,
		std::function< double(double)>	f
	)

Construct a new tabulation object.

Parameters

x_min	lower bound of tabulation domain
range	range (x_max-x_min) of tabulation domain
num	number of intervals (the number of tabulated points is actually num+1)
f	one-dimensional function f(x) which is supposed to be tabulated

Definition at line 12 of file tabulation.cc.

    : x_min_(x_min), x_max_(x_min + range), inv_dx_(num / range) {
  values_.resize(num + 1);
  const double dx = range / num;
  for (int i = 0; i <= num; i++) {
    values_[i] = f(x_min_ + i * dx);
  }
}

Member Function Documentation

get_value_step()

double smash::Tabulation::get_value_step

(

double

x

)

const

Look up a value from the tabulation (without any interpolation, simply using the closest tabulated value).

If

x is below the lower tabulation

bound we return 0, if it is above the upper bound we return the tabulated value at the upper bound.

Parameters

x	Argument to tabulated function.

Returns

Tabulated value using constant interpolation.

Definition at line 22 of file tabulation.cc.

                                                {
  if (x < x_min_) {
    return 0.;
  }
  // this rounds correctly because double -> int conversion truncates
  const unsigned int n = (x - x_min_) * inv_dx_ + 0.5;
  if (n >= values_.size()) {
    return values_.back();
  } else {
    return values_[n];
  }
}

get_value_linear()

double smash::Tabulation::get_value_linear	(	double	x,
		Extrapolation	extrapolation = Extrapolation::Linear
	)		const

Look up a value from the tabulation using linear interpolation.

If

x is below the lower bound we return 0.

If x is above the upper bound, then by default we use linear extrapolation of the two highest tabulated points. Optionally one can also extrapolate with rightmost value or zero. Linear extrapolation is not an arbitrary choice, in fact many functions tabulated in SMASH have a linear asymptotics, e.g. rho(m) functions.

Parameters

x	Argument to tabulated function.
extrapolation	Extrapolation that should be used for values outside the tabulation.

Returns

Tabulated value using linear interpolation.

Definition at line 35 of file tabulation.cc.

                                                                          {
  if (x < x_min_) {
    return 0.;
  }
  if (extrapol == Extrapolation::Zero && x > x_max_) {
    return 0.0;
  }
  if (extrapol == Extrapolation::Const && x > x_max_) {
    return values_.back();
  }
  const double index_double = (x - x_min_) * inv_dx_;
  // here n is the lower index
  const size_t n =
      std::min(static_cast<size_t>(index_double), values_.size() - 2);
  const double r = index_double - n;
  return values_[n] + (values_[n + 1] - values_[n]) * r;
}

Member Data Documentation

values_

std::vector<double> smash::Tabulation::values_

protected

vector for storing tabulated values

Definition at line 77 of file tabulation.h.

x_min_

const double smash::Tabulation::x_min_

protected

lower bound for tabulation

Definition at line 80 of file tabulation.h.

x_max_

const double smash::Tabulation::x_max_

protected

upper bound for tabulation

Definition at line 83 of file tabulation.h.

inv_dx_

const double smash::Tabulation::inv_dx_

protected

inverse step size 1/dx

Definition at line 86 of file tabulation.h.

---

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

• src/include/smash/tabulation.h
• src/tabulation.cc