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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 Analyst 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 

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, g
0.577... (mp)
3
Faraday
Faraday constant, F
9.648456 x 104 C/mole
1
FineStructure
fine structure, a
7.2973506 x 10–3
1
Gamma
Euler's constant, g
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 / 2p
1.0545887 x 10–34 J s
1
PerfectGasVolume
std. vol. ideal gas
2.241383 x 10–2 m3 / mole
1
Pi
Pi, p
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, s
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 

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

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 g is obtained and printed. Euler's constant is defined to be as follows:

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

  IDL Online Help (March 06, 2007)