newUnit

Define new unit

Syntax

c = newUnit(name,definition)

Description

c = newUnit(name,definition) defines the new unit name using the expression definition. The definition must be in terms of existing symbolic units. You cannot redefine a predefined unit or any of its alternate names.

Examples

Define New Unit and Rewrite Unit

Load the collection of symbolic units by using symunit. Find information on the predefined unit u.c_0 for the speed of light.

u = symunit;
unitInfo(u.c_0)

speed of light in vacuum - a physical unit of velocity.

Get all units for measuring 'Velocity' by calling unitInfo('Velocity').

Show that the exact value of the speed of light in SI is 299792458 metres per second.

c = unitConvert(u.c_0,'SI')

c =
299792458*([m]/[s])

Define the new unit speedOfLightApprox for the approximate value of the speed of light as 3e8 meters per second.

u = symunit;
c = newUnit('speedOfLightApprox',3e8*u.m/u.s)

c =
[speedOfLightApprox]

Alternatively, you can specify the unit by using u.speedOfLightApprox.

Define the equation E = mc² using the new unit.

syms mass
m = mass*u.kg;
E = m*c^2

E =
mass*[kg]*[speedOfLightApprox]^2

Rewrite E in terms of meters per second.

E = rewrite(E,u.m/u.s)

E =
90000000000000000*mass*(([kg]*[m]^2)/[s]^2)

Since the standard unit of energy is the joule, rewrite E in terms of Joule.

E = rewrite(E,u.Joule)

E =
90000000000000000*mass*[J]

Input Arguments

name — Name of new unit

character vector | string

Name of the new unit, specified as a character vector or string. You cannot redefine a predefined unit or any of its alternate names.

definition — Definition of new unit

symbolic expression of units

Definition of the new unit, specified as a symbolic expression of units. The new unit must be defined in terms of existing symbolic units. For example, newUnit('workday',8*u.hour), where u = symunit, defines workday as a unit representing 8 hours.

Version History

Introduced in R2017a