# PhysicalQuantity

I've always wondered why programming languages only implement the number sets used in mathematics—𝐈 (int8, uint64, etc.), 𝐂 (complex(), etc.), variations of 𝐑 (double, single, ,...), etc. To any physicist, it would make sense to have a data type that represents a physical quantity; something that has both a value (double) and a unit of measurement. Preferably, this datatype would behave intuitively for all sorts of standard operations - a Mass times a Length divided by a Time² should give a Force, according to Isaac Newton, yet that same set of operations can not ever equal an Area.

This submission is an implementation of such a datatype.

Preparations:

- put the PhysicalQuantity and PhysicalVectorQuantity directories on the

MATLAB search path, recursively

Example session:

>> L = Length(4, 'm')

L =

4 meters

>> R = Length(2, 'ft')

R =

2 feet

>> A = Area(L*R, 'm^2')

A =

2.4384e+00 square meters

Let's check: 1 ft = 0.3048 meter, so

2 ft * 4 m = 2*0.3048 * 4 = 2.4384 square meters. Cool!

Try the following:

>> A = Area(L*L*R, 'm^2')

Error using Area (line 13)

Can't create 'Area' (dimensions [L]²) from a quantity with dimensions [L]³.

>> A = Area(L*R, 'm^3')

Error using Area (line 13)

Dimensions implied by the given string ([L]³) are incompatible with those of an Area ([L]²).

>> tan( Area(L*R, 'm^2') )

Can't compute the tangent() of an Area.

Angles are dimensionless and are treated as special in this framework:

>> theta = Angle(-1.2, 'deg')

theta =

-1.2 degrees

>> cos(theta)

ans =

9.997806834748455e-01 % <- indeed the same as cosd(-1.2)

>> phi = Angle(0.5, 'rad')

phi =

500 milliradians

# Overview

In physics, a quantity's *unit* is intricately connected to the quantity itself. Typically, quantities with different units cannot be used in the same operation, without some sort of conversion between them - you can't "add apples to oranges".

This is not unlike data types in most programming languages. What do you expect to get when you divide two integers? Add a boolean to a character? You can't just do that without some sort of conversion.

Therefore, it makes sense to create a data type that takes physical units into consideration for all operations. Preferably, this data type is also super-easy to use, and produces intelligible error messages when it's used in a physically meaningless way.

And that is exactly what this tool set aims to provide.

# How to use

PysicalQuantities are constructed from scratch like this:

Q = <quantityname>(<value>, <units>)

Take a look in the PhysicalQuantity directory for an overview of currently

supported <quantities>. The <value> can be any numeric value (including

sparse, complex, etc.). The <units> should be a string specifying any of

the supported long/short unit names (see below), possibly prefixed with

an SI-multiplier (for metric units). Multiple units can be combined by the

following operations:

'*': multiply

'/': divide

'^': exponentiate

Example:

F = Force(300, 'Newton')

r = Density(2, 'kg/m^3')

To get a list of available units:

>> L = Length();

>> L.listUnits()

Length supports the following units of measurement:

- Chinese mile (li)

- Parsec (pc)

- astronomical unit (AU)

- foot (ft)

- furlong (fur)

- inch (in)

- lightyear (ly)

- meter (m)

- mile (mi)

- nautical mile (n.mi)

- smoot (smt)

- statute mile (st.mi)

- yard (yd)

- Ångström (Å)

Conversions between compatible units are seamless:

>> L = Length(20, 'yards');

>> L('meters')

ans =

1.8288e+01 meters

>> P = Length(3, 'inch');

>> Q = Length(18, 'foot');

>> Length( L*P/Q, 'meter' )

ans =

254 millimeters

Operations work as expected:

>> L = Length(1, 'inch');

>> t = Duration(32, 'seconds');

>> M = Mass(18, 'lb');

>> F = Force( M*L/t/t, 'Newton' )

ans =

2.025219058242187e+02 milliNewtons

# Note

If you observe something odd, please give me a heads up.

Preferably, raise an issue on GitHub :) Otherwise, plain ol'

email will do.

Rody Oldenhuis (2019). PhysicalQuantity (https://www.github.com/rodyo/FEX-PhysicalQuantity), GitHub. Retrieved .

1.0.0 | Updated tests, documentation and bumped version to > 0 (=ready for real-world use) |

Created with
R2018b

Compatible with R2016b to any release

Create scripts with code, output, and formatted text in a single executable document.