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.

Comments

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	[ ]
Avogadro	Avogadro's number	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]
Faraday	Faraday constant	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.