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stdlib_constants.md

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title
constants

[TOC]

Introduction

The [[stdlib_constants]] module provides mathematical constants and the most common physical constants.

Warning: The names of the most common physical constants are kept short as they are inside a dedicated module. Nonetheless, in case of overlapping names, they can always be renamed as following:

use stdlib_constants, only: clight => c

Codata

The [[stdlib_codata(module)]] module defines all codata (physical) constants as derived type. The module is automatically generated with a simple parser written in Python The latest codata constants were released in 2022 by the NIST All values for the codata constants are provided as double precision reals. The names are quite long and can be aliased with shorter names.

The derived type [[stdlib_codata_type(module):codata_constant_type(type)]] defines:

  • 4 members:

    • name (string)
    • value (double precision real)
    • uncertainty (double precision real)
    • unit (string)

  • 2 type-bound procedures:

    • print: to print the values of the constant members;
    • to_real: to get the value or the uncertainty to the desired precision.

A module level interface [[stdlib_codata_type(module):to_real(interface)]] is available for getting the constant value or uncertainty of a constant.

to_real - Get the constant value or its uncertainty.

Status

Experimental

Description

Convert a [[stdlib_codata_type(module):codata_constant_type(type)]] to a real (at least sp, or dp) scalar. Warning: Some constants cannot be converted to single precision sp reals due to the value of the exponents.

Syntax

r = [[stdlib_codata_type(module):to_real(interface)]] (c, mold [, uncertainty])

Arguments

c: argument has intent(in) and shall be of type [[stdlib_codata_type(module):codata_constant_type(type)]].

mold: argument has intent(in) and shall be of real type. Note: The type of the mold argument defines the type of the result.

uncertainty (optional): argument has intent(in) and shall be of logical type. It specifies if the uncertainty needs to be returned instead of the value. Default to .false..

Return value

Returns a scalar of real type which is either the value or the uncertainty of a codata constant.

Example

{!example/constants/example_constants.f90!}