C Library Functions  - M_constants (3)

NAME
M_constants(3f) - [M_constants:INTRO] Useful constants

CONTENTS

Synopsis
Description
     Universal Constants
     Physical Constants
Notes
Example

SYNOPSIS
use M_constants,
  only : uc 
      ! real128 constants
      uc%qp%pi
      uc%qp%gamma
      uc%qp%e
      uc%qp%golden_ratio
      uc%qp%euler


      ! real64 constants
      uc%dp%pi
      uc%dp%gamma
      uc%dp%e
      uc%dp%golden_ratio
      uc%dp%euler


      ! real32 constants
      uc%sp%pi
      uc%sp%gamma
      uc%sp%e
      uc%sp%golden_ratio
      uc%sp%euler
use M_constants,
  only : fmt ! formats fmt%all fmt%commas
use M_constants,
  only : lets ! ASCII character set strings lets%upper lets%lower lets%hexadecimal lets%digits
use M_constants,
  only : calen ! English Civil Calendar names calen%months calen%mths calen%weekdays calen%wkds

DESCRIPTION
Useful universal constants, physical constants, formats, ...

    UNIVERSAL CONSTANTS

e The base of the natural logarithm system. "e" was named in honor of Euler, but is known as Napier’s constant. "euler"
gamma The Euler-Mascheroni constant is often denoted by a lower-case Gamma.
golden_ratio
  In mathematics, two quantities are in the golden ratio if their ratio is the same as the ratio of their sum to the larger of the two quantities. so for a > b > 0, (a + b)/ a = a/b where the Greek letter phi often denotes the golden ratio.
pi The ratio of the circumference of a circle to the diameter of the circle

    PHYSICAL CONSTANTS

"deg_per_rad" "rad_per_deg"
c__m_per_sec
  Speed of light in a vacuum
c__ft_per_sec
  Speed of light in a vacuum

NOTES

Gamma is defined as 

   Gamma = limit ( M -> Infinity ) ( Sum ( 1 <= N <= M ) 1 / N ) - Log ( M )

EXAMPLE
Sample program: 

   program demo_M_constants
   use, intrinsic :: iso_fortran_env, only : stdout=>OUTPUT_UNIT
   use M_constants, only : uc, fmt, lets, calen
   implicit none
   ! give a local name to a constant:
   ! universal constant, single-precision, e
   real,parameter             :: e=uc%sp%e
   character(len=*),parameter :: all=fmt%all
   integer                    :: i


      ! or just use full name
      ! universal constant, quad-precision, gamma
      print fmt%all, ’gamma=’,uc%qp%gamma
      print all, ’e=’,e
      !
      ! or rename it with ASSOCIATE
      associate (gamma => uc%dp%gamma)
         print all,’gamma=’,gamma
      end associate
      !
      ! string constants:
      !
      ! strings of letter sets
      print all,’lets%upper=’,lets%upper
      print all,’lets%lower=’,lets%lower
      print all,’lets%hexadecimal=’,lets%hexadecimal
      print all,’lets%digits=’,lets%digits
      !
      ! English civil calendar names
      print fmt%commas,’calen%months=’,new_line(’a’),(calen%months(i:i+2) &
             & ,new_line(’a’),i=1,size(calen%months),3)
      print fmt%commas,’calen%mths=’,calen%mths
      print fmt%commas,’calen%weekdays=’,&
              & (trim(calen%weekdays(i)),i=1,size(calen%weekdays))
      print fmt%commas,’calen%wkds=’,calen%wkds


   end program demo_M_constants
Results: 

 > gamma= 0.577215664901532860606512090082402471
 > e= 2.71828175
 > gamma= 0.57721566490153287
 > lets%upper= ABCDEFGHIJKLMNOPQRSTUVWXYZ
 > lets%lower= abcdefghijklmnopqrstuvwxyz
 > lets%hexadecimal= ABCDEFabcdef0123456789
 > lets%digits= 0123456789
 > calen%months=,
 > ,January  ,February ,March    ,
 > ,April    ,May      ,June     ,
 > ,July     ,August   ,September,
 > ,October  ,November ,December ,
 >
 > calen%mths=,Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec
 > calen%weekdays=,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Sunday
 > calen%wkds=,Mon,Tue,Wed,Thu,Fri,Sat,Sun

Nemo Release 3.1 M_constants (3) February 23, 2025
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