IMSL_CONSTANT

Syntax | Return Value | Arguments | Keywords | Discussion | Examples | Errors | Version History

The IMSL_CONSTANT function returns the value of various mathematical and physical constants.

Note
This routine requires an IDL Advanced Math and Stats license. For more information, contact your ITT Visual Information Solutions sales or technical support representative.

Syntax

Result = IMSL_CONSTANT(name[, units] [, /DOUBLE])

Return Value

By default, returns the desired constant. If no value can be computed, NaN (Not a Number) is returned.

Arguments

name

Scalar string specifying the name of the desired constant. The case of the characters is not relevant when specifying name, i.e., character strings "PI", "Pi", "pI", and "pi" are equivalent. Spaces and underscores are allowed and ignored.

units

Scalar string specifying the units of the desired constant. If empty, then Systeme International d'Unites (SI) units are assumed. The case of the characters is not relevant when specifying units, i.e., character strings "METER", "Meter", and "meter" are equivalent. Parameter units has the form "U1*U2*...*Um/V1/.../Vn," where Ui and Vi are the names of basic units or 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".

Keywords

DOUBLE

If present and nonzero, double precision is used.

Discussion

The names allowed are listed in Table 25-1. Values marked with (mp) are exact (to machine precision). The references in the right-hand column are indicated by code numbers: (1) for Cohen and Taylor (1986), (2) for Liepman (1964), and (3) for precomputed mathematical constants. The supported units are listed in Table 25-2.

Table 25-1: Constant Names 

Name
Description
Value
Ref.

amu

atomic mass unit

1.6605655 x 10–27 kg

1

ATM

standard atm. pressure

1.01325 x 105 N/m2 (mp)

2

AU

astronomical unit

1.496 x 1011 m

Avogadro

Avogadro's number, N

6.022045 x 1023 1/mole

1

Boltzman

Boltzman's constant, k

1.380662 x 10–23 J / K

1

C

speed of light, c

2.997924580 x 108 m/s

1

Catalan

Catalan's constant

0.915965... (mp)

3

E

base of natural logs, e

2.718... (mp)

3

ElectronCharge

electron charge, e

1.6021892 x 10–19 C

1

ElectronMass

electron mass, me

9.109534 x 10–31 kg

1

ElectronVolt

electron volt, ev

1.6021892 x 10–19 J

1

Euler

Euler's constant, γ

0.577... (mp)

3

Faraday

Faraday constant, F

9.648456 x 104 C/mole

1

FineStructure

fine structure, α

7.2973506 x 10–3

1

Gamma

Euler's constant, γ

0.577... (mp)

3

Gas

gas constant, R0

8.31441 J/mole/K

1

Gravity

gravitational constant, G

6.6720 x 10–11 N m2 / kg2

1

Hbar

Planck's constant / 2π

1.0545887 x 10–34 J s

1

PerfectGasVolume

std. vol. ideal gas

2.241383 x 10–2 m3 / mole

1

Pi

Pi, π

3.141... (mp)

3

Planck

Planck's constant, h

6.626176 x 10–34 J s

1

ProtonMass

proton mass, Mp

1.6726485 x 10–27 kg

1

Rydberg

Rydberg's constant, Rinfinity

1.097373177 x 107 /m

1

Speedlight

speed of light, c

2.997924580 x 108 m/s

1

StandardGravity

standard g

9.80665 m/s2 (mp)

2

StandardPressure

standard atm. pressure

1.01325 x 105 N/m2 (mp)

2

StefanBoltzman

Stefan-Boltzman, σ

5.67032 x 10–8 W/K4 /m2

1

WaterTriple

triple point of water

2.7316 x 102 K

2

The units allowed are as follows:

Table 25-2: Supported Units 

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

l = 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 = Tesla, Wb = Weber

other units

l, farad, mole, Gauss, Henry, Maxwell, Ohm

The metric prefixes listed in Table 25-3 can be used with the previous units. The one- or two-letter prefixes can only be used with one-letter unit abbreviations.

Table 25-3: Supported Prefixes

Prefix
Definition
Value

a

atto

10–18

f

femto

10–15

p

pico

10–12

n

nano

10–9

u

micro

10–6

m

milli

10–3

c

centi

10–2

d

deci

10–1

dk

deca

102

k

kilo

103

myria

104

mega

106

g

giga

109

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 as follows:

IMSL_CONSTANT-07.jpg

PM, IMSL_CONSTANT('gamma') 
 
0.577216

Example 2

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

c1 = IMSL_CONSTANT('SpeedLight', 'meter/second') 
c2 = IMSL_CONSTANT('SpeedLight', 'mile/second') 
c3 = IMSL_CONSTANT('SpeedLight', 'cm/ns') 
PM, 'speed of light = ', c1, c2, c3, $ 
   Title ='             meters/second   ' + $ 
   'miles/second     cm/ns' 
 
meters/second   miles/second     cm/ns 
speed of light =  2.99792e+008      186282.      29.9792

Errors

Warning Errors

MATH_MASS_TO_FORCE—Conversion of units-of-mass to units-of-force required for consistency.

Version History

6.4

Introduced