smash::Tabulation Class Reference

#include <tabulation.h>

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

Definition at line 30 of file tabulation.h.

Collaboration diagram for smash::Tabulation:

Public Member Functions
	Tabulation ()
	Construct an empty tabulation object. More...
	Tabulation (double x_min, double range, size_t num, std::function< double(double)> f)
	Construct a new tabulation object. More...
bool	is_empty () const
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, ExtrapolationType extrapolation=ExtrapolationType::Linear) const
	Look up a value from the tabulation using linear interpolation. More...
void	write (std::ofstream &stream, sha256::Hash hash) const
	Write a binary representation of the tabulation to a stream. More...

Static Public Member Functions
static Tabulation	from_file (std::ifstream &stream, sha256::Hash hash)
	Construct a tabulation object by reading binary data from a stream. More...

Private Member Functions
double	linear_approximation_ (double x) const
	Linear approximation to interpolate and extrapolate tabulations. More...

Private Attributes
std::vector< double >	values_ {}
	vector for storing tabulated values More...
double	x_min_ = smash_NaN<double>
	lower bound for tabulation More...
double	x_max_ = smash_NaN<double>
	upper bound for tabulation More...
double	inv_dx_ = smash_NaN<double>
	inverse step size 1/dx More...

Constructor & Destructor Documentation

Tabulation() [1/2]

smash::Tabulation::Tabulation ( )

inline

Construct an empty tabulation object.

Definition at line 35 of file tabulation.h.

: values_({}), x_min_(0.0), x_max_(0.0), inv_dx_(0.0) {}

Tabulation() [2/2]

smash::Tabulation::Tabulation	(	double	x_min,
		double	range,
		size_t	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

Returns

Construct object.

Exceptions

if	less than two values are tabulated.

Definition at line 14 of file tabulation.cc.

    : x_min_(x_min), x_max_(x_min + range), inv_dx_(num / range) {
  if (num < 2) {
    throw std::runtime_error("Tabulation needs at least two values");
  }
  values_.resize(num + 1);
  const double dx = range / num;
  for (size_t i = 0; i <= num; i++) {
    values_[i] = f(x_min_ + i * dx);
  }
}

Member Function Documentation

is_empty()

bool smash::Tabulation::is_empty ( ) const

inline

Returns

whether the tabulation is empty.

Definition at line 54 of file tabulation.h.

{ return values_.empty(); }

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from_file()

Tabulation smash::Tabulation::from_file ( std::ifstream &  stream, sha256::Hash  hash  )

static

Construct a tabulation object by reading binary data from a stream.

Parameters

stream	Stream containing the binary representation of the tabulation.
hash	Hash corresponding to the particle properties for which the tabulation was created.

Returns

(true, tabulation) if the given hash matches the one given by the stream, (false, empty) otherwise.

Definition at line 176 of file tabulation.cc.

                                                                     {
  sha256::Hash hash_from_stream = sread_hash(stream);
  Tabulation t;
  if (hash != hash_from_stream) {
    return t;
  }
  t.x_min_ = sread_double(stream);
  t.x_max_ = sread_double(stream);
  t.inv_dx_ = sread_double(stream);
  t.values_ = sread_vector(stream);
  return t;
}

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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 27 of file tabulation.cc.

                                                {
  if (x < x_min_) {
    return 0.;
  }
  const unsigned int n =
      numeric_cast<unsigned int>(std::floor((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,
		ExtrapolationType	extrapolation = ExtrapolationType::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 type that is used for values greater than the maximum x in the tabulation.

Returns

Tabulated value using linear interpolation.

Exceptions

std::invalid_argument

if unsupported extrapolation type is requested.

Definition at line 40 of file tabulation.cc.

                                                                            {
  if (x < x_min_) {
    return 0.;
  }
  switch (extrapolation_type_for_x_beyond_xmax) {
    case ExtrapolationType::Zero:
      if (x > x_max_) {
        return 0.;
      }
      [[fallthrough]];
    case ExtrapolationType::Constant:
      if (x > x_max_) {
        return values_.back();
      }
      [[fallthrough]];
    case ExtrapolationType::Linear:
      return linear_approximation_(x);
    default:
      throw std::invalid_argument(
          "The provided extrapolation type is not supported. Valid types are "
          "'Zero', 'Constant', and 'Linear'.");
  }
}

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write()

void smash::Tabulation::write	(	std::ofstream &	stream,
		sha256::Hash	hash
	)		const

Write a binary representation of the tabulation to a stream.

Parameters

stream	Stream to which the binary representation is written.
hash	Hash corresponding to the particle properties for which the tabulation was created.

Definition at line 168 of file tabulation.cc.

                                                                 {
  swrite(stream, hash);
  swrite(stream, x_min_);
  swrite(stream, x_max_);
  swrite(stream, inv_dx_);
  swrite(stream, values_);
}

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linear_approximation_()

double smash::Tabulation::linear_approximation_ ( double  x ) const

inlineprivate

Linear approximation to interpolate and extrapolate tabulations.

Definition at line 120 of file tabulation.h.

                                               {
    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;
  }

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Member Data Documentation

values_

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

private

vector for storing tabulated values

Definition at line 108 of file tabulation.h.

x_min_

double smash::Tabulation::x_min_ = smash_NaN<double>

private

lower bound for tabulation

Definition at line 111 of file tabulation.h.

x_max_

double smash::Tabulation::x_max_ = smash_NaN<double>

private

upper bound for tabulation

Definition at line 114 of file tabulation.h.

inv_dx_

double smash::Tabulation::inv_dx_ = smash_NaN<double>

private

inverse step size 1/dx

Definition at line 117 of file tabulation.h.

---

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

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