Overview

Created on Fri May 1 11:52:42 2020

@author: Reuben

This section provides an overview of how the unitty package works.

Quantities and Units classes

The foundational class in unitty is the Quantity. A Unit is a special type of Quantity that also has an abbreviation and name. Units also display a little differenty.

Each Quantity contains:

  • value: A float representing the magnitude of the quantity in terms of base dimensions (length, time, mass, etc)
  • spec: A list of signed integers. For simple units, there will be only one integer. For compound units (e.g. m/s), there will be more than one. The integers correspond to other Quantities. Positive integers indicate the are multiplied, while negative integers indicate they are divided.
  • vector: Each base dimensions is independent, and the exponent for each base dimension is represented as a number. This vectore is an array of such numbers for all base dimensions. This allows quick and robust dimensionality checking.
  • abbr [optional]: The abbreviation of the Quantity (usually for Units)
  • name [optional]: The name of the Quantity (usually for Units)
  • parent [optional]: The name of the Units instance it belongs to. This is important, since otherwise the spec doesn’t make any sense.

The Units class

A Units instance contains all of the Units that you might want to work with at the same time. The Units class holds:

  • The Unit instances
  • Mappings between string abbreviations for those units and the integers that match them.
  • A mapping of the base type (length, time, etc) for each unit.

The System class

This class contains information about a particular unit system. It is responsible for processing a given Quantity to give the correct value and unit string for that unit system. The magnitudes in all Quantity instances correspond to the base dimensions, and systems allow different those magnitudes to be expressed in different units. For example, 1 ‘length’ might be expressed as 1 meter in the metric system, but 3.28083 feet in the imperial US system.

System instances contain information about:

  • The preferred units to use in the system for each base type. For example, the length dimension in the metric system might use um, mm, m, and km. A US system might specifiy units of inch, ft, and mile for length.
  • How to apply the preferred units to express Quantities in those units.

The Systems class

The Systems class contains all the different systems that you might want to switch between. It is provides a way to set up those different systems from specification files.

Systems instances know which system is active, and direct methods to express quantities to methods in that active system.

Functions

unitty provides a number of functions. These are documented in the namespace module.