FNLMath : Utilities : CONST
CONST
This function returns the value of various mathematical and physical constants.
Function Return Value
CONST — Value of the constant. (Output)
See Comment 1.
Required Arguments
NAME — Character string containing the name of the desired constant. (Input)
See Comment 3 for a list of valid constants.
FORTRAN 90 Interface
Generic: CONST (NAME)
Specific: The specific interface names are S_CONST and D_CONST.
FORTRAN 77 Interface
Single: CONST (NAME)
Double: The double precision name is DCONST.
Description
Routine CONST returns the value of various mathematical and physical quantities. For all of the physical values, the Systeme International d’Unites (SI) are used.
The reference for constants are indicated by the code in [ ] Comment above.
[1] Cohen and Taylor (1986)
[2] Liepman (1964)
[3] Precomputed mathematical constants
The constants marked with an E before the [ ] are exact (to machine precision).
To change the units of the values returned by CONST, see CUNIT.
1. If the generic version of this function is used, the immediate result must be stored in a variable before use in an expression. For example:
X = CONST(‘PI’)
Y = COS(x)
must be used rather than
Y = COS(CONST(‘PI’)).
If this is too much of a restriction on the programmer, then the specific name can be used without this restriction.
2. The case of the character string in NAME does not matter. The names “PI”, “Pi”, “Pi”, and “pi” are equivalent.
3. The units of the physical constants are in SI units (meter kilogram-second).
4. The names allowed are as follows:
Name
Description
Value
Ref.
AMU
Atomic mass unit
1.6605402E 27 kg
[1]
ATM
Standard atm pressure
1.01325E + 5N/m2E
[2]
AU
Astronomical unit
1.496E + 11m
[ ]
6.0221367E + 231/mole
[1]
Boltzman
Boltzman's constant
1.380658E 23J/K
[1]
C
Speed of light
2.997924580E + 8m/sE
[1]
Catalan
Catalan's constant
0.915965 … E
[3]
E
Base of natural logs
2.718…E
[3]
ElectronCharge
Electron change
1.60217733E 19C
[1]
ElectronMass
Electron mass
9.1093897E 31 kg
[1]
ElectronVolt
Electron volt
1.60217733E 19J
[1]
Euler
Euler's constant gamma
0.577 … E
[3]
9.6485309E + 4C/mole
[1]
FineStructure
fine structure
7.29735308E 3
[1]
Gamma
Euler's constant
0.577 … E
[3]
Gas
Gas constant
8.314510J/mole/k
[1]
Gravity
Gravitational constant
6.67259E 11N * m2/kg2
[1]
Hbar
Planck constant / 2 pi
1.05457266E 34J * s
[1]
PerfectGasVolume
Std vol ideal gas
2.241383E 2m3/mole
[*]
Pi
Pi
3.141 … E
[3]
Planck
Planck's constant h
6.6260755E 34J * s
[1]
ProtonMass
Proton mass
1.6726231E 27 kg
[1]
Rydberg
Rydberg's constant
1.0973731534E + 7/m
[1]
SpeedLight
Speed of light
2.997924580E + 8m/s E
[1]
StandardGravity
Standard g
9.80665m/s2E
[2]
StandardPressure
Standard atm pressure
1.01325E + 5N/m2E
[2]
StefanBoltzmann
Stefan-Boltzman
5.67051E 8W/K4/m2
[1]
WaterTriple
Triple point of water
2.7316E + 2K E
[2]
Example
In this example, Euler’s constant γ is obtained and printed. Euler’s constant is defined to be

USE CONST_INT
USE UMACH_INT

IMPLICIT NONE
INTEGER NOUT
REAL GAMA
! Get output unit number
CALL UMACH (2, NOUT)
! Get gamma
GAMA = CONST('GAMMA')
! Print gamma
WRITE (NOUT,*) 'GAMMA = ', GAMA
END
Output

GAMMA = 0.5772157
For another example, see CUNIT.