FAQ.md

Frequently Asked Questions

• What is the difference between id and name?
• Why are certain constants included but others are not?
• Why are certain entries empty?
• Do I need the Symbolic Math Toolbox to use Constants?

What is the difference between id and name?

The id is the constant's current name, while name provides its historical name. The id remains fixed, but the name of a given constant may change between datasets.

const = Constants('all', 'all');

% Get the current name
const.epsilonzero.id
% >> 'vacuum electric permittivity'

% Get historical names from 1998-2018 datasets
const.epsilonzero.name(1:6)
% >> "electric constant"    "electric constant"    "electric constant"...
% >> "electric constant"    "electric constant"    "vacuum electric permittivity"

Why are certain constants included but others are not?

The Constants object contains constants with dedicated symbols specified by CODATA but excludes derived or assembled constants without unique symbols.

For example, the electron mass (m_e) and elementary charge (e) have dedicated symbols and are included in Constants, but the electron charge to mass quotient, -e / m_e, is not included since it does not have a unique symbol.

Why are certain entries empty?

Entries are empty in individually loaded datasets if the constant does not exist in the dataset.

For example, the value of the Faraday constant for conventional electric current (F^*) is not listed in the 2018 dataset, so it will be empty when loading that specific dataset:

const = Constants('all', '2018');
const.Fstar
% >> []

Do I need the Symbolic Math Toolbox to use Constants?

No. Constants will work just fine without the Symbolic Math Toolbox. However, the symvalue, symunit, and sym options will only be available if the Symbolic Math Toolbox is present.