SimpleConstants defines the values of some fundamental constants of physics in SI units. PhysicalConstants provides a complete set of fundamental constants with units, but in many cases of writing scientific code we care only about the values of the fundamental constants without units. SimpleConstants is a lightweight package defining those values.

SimpleConstants utilizes Unicode symbols as much as possible to define compact symbols to store the fundamental constants (e.g., ε₀ instead of eps_0 or ε_0). It further promotes compactness by defining compound constants that are products of fundamental constants that frequently appear in equations. For example,

• the package defines πc₀ = π * c₀, with which the angular frequency of an electromagnetic wave of wavelength λ can be written ω = 2πc₀ / λ instead of ω = 2π * c₀ / λ;
• the package defines i2π = im * 2π, with which the complex exponential of an angle 120° can be written exp(i2π/3) instead of exp(im * 2π / 3); etc.

SimpleConstants also defines all the SI prefixes (e.g., kilo and milli). Unitful provides a complete set of those prefixes together with other units, but again, SimpleConstants is a lightweight package defining those prefixes. Here is a simple example to convert a wavelength of 1.55 µm to a nm-value:

using SimpleConstants
λ = 1.55micro
λunit = nano
println("λ = $(round(λ/λunit, sigdigits=3)) $(λunit)m.")  # print out "λ = 1550.0 nm."