constant

Returns the value of various mathematical and physical constants.

Synopsis

#include <imsl.h>

float imsl_f_constant (char *name, char *unit)

The type double function is imsl_d_constant.

Required Arguments

char *name (Input)
Character string containing the name of the desired constant. The case of the character string name does not matter. The names “PI”, “Pi”, “pI”, and “pi” are equivalent. Spaces and underscores are allowed and ignored.

char *unit (Input)
Character string containing the units of the desired constant. If NULL, then Système International d’Unités (SI) units are assumed. The case of the character string unit does not matter. The names “METER”, “Meter” and “meter” are equivalent. unit has the form U1*U2*... *Um/V1/.../Vn, where Ui and Vi are the names of basic units or are the names of basic units raised to a power. Basic units must be separated by * or /. Powers are indicated by ^, as in “m^2” for m2. Examples are, “METER*KILOGRAM/SECOND”, “M*KG/S”, “METER”, or “M/KG^2”.

Return Value

By default, imsl_f_constant returns the desired constant. If no value can be computed, NaN is returned.

 

Description

The names allowed are listed in the following table. Values marked with a ‡ are exact (to machine precision). The references in the right-hand column are indicated by the code numbers: [1] for Cohen and Taylor (1986), [2] for Liepman (1964), and [3] for precomputed mathematical constants.

Name	Description	Value	Reference
Amu	Atomic mass unit	1.6605655 × 10-27 kg	1
ATM	Standard atm pressure	1.01325 × 105 N/m2 ‡	2
AU	Astronomical unit	1.496 × 1011 m
Avogadro	Avogadro's number, N	6.022045 × 1023 1/mole	1
Boltzman	Boltzman's constant, k	1.380662 × 10-23 J/K	1
C	Speed of light, c	2.997924580 × 108 m/s	1
Catalan	Catalan's constant	0.915965…‡	3
E	Base of natural logs, e	2.718…‡	3
ElectronCharge	Electron charge, e	1.6021892 × 10-19 C	1
ElectronMass	Electron mass, me	9.109534 × 10-31 kg	1
ElectronVolt Euler	ElectronVolt, ev Euler's constant, γ	1.6021892 x10 -19J 0.577…‡	1 3
Faraday	Faraday constant, F	9.648456 × 104 C/mole	1
FineStructure	Fine structure, α	7.2973506 ×10-3	1
Gamma	Euler's constant, γ	0.577…‡	3
Gas	Gas constant, R0	8.31441 J/mole/K	1
Gravity	Gravitational constant, G	6.6720 × 10-11 N m2/kg2	1
Hbar	Planck's constant/2π	1.0545887 × 10-34 J s	1
PerfectGasVolume	Std vol ideal gas	2.241383 × 10-2 m3/mole	1
Pi	Pi, π	3.141…‡	3
Planck	Planck's constant, h	6.626176 × 10-34 J s	1
ProtonMass	Proton mass, Mp	1.6726485 × 10-27 kg	1
Rydberg	Rydberg's constant, Rμ	1.097373177 × 107/m	1
Speedlight	Speed of light, c	2.997924580 ×108 m/s	1
StandardGravity	Standard g	9.80665 m/s2 ‡	2
StandardPressure	Standard atm pressure	1.01325 ×105 N/m2 ‡	2
StefanBoltzman	Stefan-Boltzman, σ	5.67032 × 10-8W/K4/m2	1
WaterTriple	Triple point of water	2.7316× 102 K	2

The units allowed are as follows:

Unit	Description
Time	day, hour = hr, min, minute, s = sec = second, year
Frequency	Hertz = Hz
Mass	AMU, g = gram, lb = pound, ounce = oz, slug
Distance	Angstrom, AU, feet = foot, in = inch, m = meter = metre, micron, mile, mill, parsec, yard
Area	Acre
Volume	1 = liter=litre
Force	dyne, N = Newton
Energy	BTU, Erg, J = Joule
Work	W = watt
Pressure	ATM = atmosphere, bar
Temperature	degC = Celsius, degF = Fahrenheit, degK = Kelvin
Viscosity	poise, stoke
Charge	Abcoulomb, C = Coulomb, statcoulomb
Current	A = ampere, abampere, statampere
Voltage	Abvolt, V = volt
Magnetic induction	T = Telsa, Wb = Weber
Other units	I, farad, mole, Gauss, Henry, Maxwell, Ohm

The following metric prefixes may be used with the above units. The one or two letter prefixes may only be used with one letter unit abbreviations.

A	atto	10-18	d	deci	10-1
F	femto	10-15	dk	deca	102
P	pico	10-12	k	kilo	103
N	nano	10-9		myria	104
U	micro	10-6		mega	106
M	milli	10-3	g	giga	109
C	centi	10-2	t	tera	1012

There is no one letter unit abbreviation for myria or mega since m means milli.

Examples

 

Example 1

In this example, Euler’s constant γ is obtained and printed. Euler’s constant is defined to be

 

 

 

#include <stdio.h>

#include <imsl.h>

 

int main()

{

float gamma;

/* Get gamma */

gamma = imsl_f_constant("gamma", 0);

/* Print gamma */

printf("gamma = %f\n", gamma);

}

Output

 

gamma = 0.577216

Example 2

In this example, the speed of light is obtained using several different units.

 

#include <stdio.h>

#include <imsl.h>

 

int main()

{

float speed_light;

/* Get speed of light in meters/second */

speed_light = imsl_f_constant("Speed Light", "meter/second");

printf("speed of light = %g meter/second\n", speed_light);

/* Get speed of light in miles/second */

speed_light = imsl_f_constant("Speed Light", "mile/second");

printf("speed of light = %g mile/second\n", speed_light);

/* Get speed of light in */

/* centimeters/nanosecond */

speed_light = imsl_f_constant("Speed Light", "cm/ns");

printf("speed of light = %g cm/ns\n", speed_light);

}

Output

 

speed of light = 2.99792e+08 meter/second

speed of light = 186282 mile/second

speed of light = 29.9793 cm/ns

Warning Errors

IMSL_MASS_TO_FORCE

A conversion of units of mass to units of force was required for consistency.