What is n::Bool in the Quaternion constructor?

[homocomputeris]

What is n::Bool=false in the Quaternion constructor? What does it represent?

[goretkin]

The Quaternion type is defined here:

Quaternions.jl/src/Quaternion.jl

Lines 1 to 7 in 01d45b4

	struct Quaternion{T<:Real} <: Number
	s::T
	v1::T
	v2::T
	v3::T
	norm::Bool
	end

It includes a field to indicate whether the quaternion has unit length. The killer app for quaternions is that a unit-length quaternion can represent a rotations in 3D. You might think of it as a way to cache the computation of computing the length.

FYI, not many libraries implement quaternions in this way from what I see.

[homocomputeris]

The problem with this implementation is (or was, at least) that one could create a non-unit quaternion and set norm=True, basically making the argument useless.

[goretkin]

The point is to avoid unnecessary computation, so I don't see a way around that problem.

[homocomputeris]

The constructor should check it a passed quadruple can represent a unit quaternion.

[goretkin]

That "check" is exactly the unnecessary computation I mean. There are cases where you know that the quadruple has unit length. For example, if you wanted to ignore floating point issues, you might want to assert that multiplying two unit-length quaternions produces a unit-length quaternion.

[hyrodium]

The .norm field will be removed in #75, and it will not be documented.