Remove DualQuaternion

Project.toml

@@ -1,19 +1,16 @@
 name = "Quaternions"
 uuid = "94ee1d12-ae83-5a48-8b1c-48b8ff168ae0"
-version = "0.5.6"
+version = "0.6.0-DEV"
 
 [deps]
-DualNumbers = "fa6b7ba4-c1ee-5f82-b5fc-ecf0adba8f74"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 
 [compat]
-DualNumbers = "0.5, 0.6"
 julia = "1"
 
 [extras]
-ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["ForwardDiff", "Test"]
+test = ["Test"]

docs/Project.toml

@@ -1,2 +1,7 @@
 [deps]
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
+ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
+Quaternions = "94ee1d12-ae83-5a48-8b1c-48b8ff168ae0"
+
+[compat]
+ForwardDiff = "0.10"

docs/make.jl

@@ -14,6 +14,7 @@ makedocs(;
     ),
     pages=[
         "Home" => "index.md",
+        "Examples" => ["examples/dual_quaternions.md"],
     ],
 )
 

docs/src/examples/dual_quaternions.md

@@ -0,0 +1,159 @@
+# Dual quaternions
+
+## Introduction
+
+The [dual quaternions](https://en.wikipedia.org/wiki/Dual_quaternion) are an example of "biquaternions."
+They can be represented equivalently either as a [dual number](https://en.wikipedia.org/wiki/Dual_number) where both both the "primal" and "tangent" part are quaternions
+
+```math
+d = q_0 + q_e \epsilon = (s_0 + a_0 i + b_0 j + c_0 k) + (s_e + a_e i + b_e j + c_e k) \epsilon
+```
+
+or as a quaternion where the scalar part and three imaginary parts are all dual numbers
+
+```math
+d = s + ai + bj + ck = (s_0 + s_e \epsilon) + (a_0 + a_e \epsilon) i + (b_0 + b_e \epsilon) j + (c_0 + c_e \epsilon) k.
+```
+
+Like unit quaternions can compactly representation rotations in 3D space, dual quaternions can compactly represent rigid transformations (rotation with translation).
+
+Without any special glue code, we can construct a dual quaternion by composing `ForwardDiff.Dual` and [`Quaternion`](@ref); this uses the second representation described above:
+
+!!! note
+    Previously this package contained a specialized `DualQuaternion` type.
+    This was removed in v0.6.0 because offered nothing extra over composing [ForwardDiff](https://github.com/JuliaDiff/ForwardDiff.jl) and Quaternions.
+
+## Utility functions
+
+First let's load the packages:
+
+```@example dualquat
+using ForwardDiff, Quaternions, Random
+```
+
+Then we'll create some utility types/functions:
+
+```@example dualquat
+const DualQuaternion{T} = Quaternion{ForwardDiff.Dual{Nothing,T,1}}
+
+purequat(p::AbstractVector) = quat(false, @views(p[begin:begin+2])...)
+
+dual(x::Real, v::Real) = ForwardDiff.Dual(x, v)
+
+function dualquat(_q0::Union{Real,Quaternion}, _qe::Union{Real,Quaternion})
+    q0 = quat(_q0)
+    qe = quat(_qe)
+    Quaternion(
+        dual(real(q0), real(qe)),
+        dual.(imag_part(q0), imag_part(qe))...,
+    )
+end
+
+function primal(d::DualQuaternion)
+    return Quaternion(
+        ForwardDiff.value(real(d)),
+        ForwardDiff.value.(imag_part(d))...,
+    )
+end
+
+function tangent(d::DualQuaternion)
+    return Quaternion(
+        ForwardDiff.partials(real(d), 1),
+        ForwardDiff.partials.(imag_part(d), 1)...,
+    )
+end
+
+function Base.conj(d::DualQuaternion, type::Int)
+    type == 1 && return conj(d)
+    type == 2 && return dualquat(primal(d), -tangent(d))
+    de = tangent(d)
+    type == 3 && return dualquat(conj(primal(d)), quat(-de.s, imag_part(de)...))
+    throw(ArgumentError("type=$type is not recognized. type must be in {1,2,3}."))
+end
+
+rotation_part(d::DualQuaternion) = primal(d)
+
+translation_part(d::DualQuaternion) = dualquat(true, conj(rotation_part(d)) * tangent(d))
+
+# first=true returns the translation performed before the rotation: R(p+t)
+# first=false returns the translation performed after the rotation: R(p)+t
+function translation(d::DualQuaternion; first::Bool=true)
+    v = first ? primal(d)' * tangent(d) : tangent(d) * primal(d)'
+    return collect(2 .* imag_part(v))
+end
+
+function transform(d::DualQuaternion, p::AbstractVector)
+    dp = dualquat(true, purequat(p))
+    dpnew = d * dp * conj(d, 3)
+    pnew_parts = imag_part(tangent(dpnew))
+    pnew = similar(p, eltype(pnew_parts))
+    pnew .= pnew_parts
+    return pnew
+end
+
+function transformationmatrix(d::DualQuaternion)
+    R = rotationmatrix(rotation_part(d))
+    t = translation(d; first=false)
+    T = similar(R, 4, 4)
+    T[1:3, 1:3] .= R
+    T[1:3, 4] .= t
+    T[4, 1:3] .= 0
+    T[4, 4] = 1
+    return T
+end
+
+randdualquat(rng::AbstractRNG,T=Float64) = dualquat(rand(rng, Quaternion{T}), rand(rng, Quaternion{T}))
+randdualquat(T=Float64) = randdualquat(Random.GLOBAL_RNG,T)
+```
+
+## Example: transforming a point
+
+Now we'll create a dual quaternion.
+```@example dualquat
+x = sign(randdualquat())
+```
+
+`sign(q) == q / abs(q)` both normalizes the primal part of the dual quaternion and makes the tangent part perpendicular to it.
+
+```@example dualquat
+abs(primal(x)) ≈ 1
+isapprox(real(primal(x)' * tangent(x)), 0; atol=1e-10)
+```
+
+Here's how we use dual quaternions to transform a point:
+
+```@example dualquat
+p = randn(3)
+```
+
+```@example
+transform(x, p)
+```
+
+We can check that this gives the same result as transforming with an affine transformation matrix:
+
+```@example dualquat
+transform(x, p) ≈ (transformationmatrix(x) * vcat(p, 1))[1:3]
+```
+
+## Example: motion planning
+
+For unit quaternions, spherical linear interpolation with [`slerp`](@ref) can be used to interpolate between two rotations with unit quaternions, which can be used to plan motion between two orientations.
+Similarly, we can interpolate between unit dual quaternions to plan motion between two rigid poses.
+Conveniently, we can do this using the exact same `slerp` implementation.
+
+```@example dualquat
+y = sign(randdualquat())
+```
+
+```@example dualquat
+slerp(x, y, 0) ≈ x
+```
+
+```@example dualquat
+slerp(x, y, 1) ≈ y
+```
+
+```@example dualquat
+slerp(x, y, 0.3)
+```

docs/src/index.md

@@ -1,6 +1,6 @@
 # Quaternions.jl
 
-A Julia package implementing [quaternions](https://en.wikipedia.org/wiki/Quaternion), [octonions](https://en.wikipedia.org/wiki/Octonion) and [dual-quaternions](https://en.wikipedia.org/wiki/Dual_quaternion)
+A Julia package implementing [quaternions](https://en.wikipedia.org/wiki/Quaternion) and [octonions](https://en.wikipedia.org/wiki/Octonion).
 
 !!! note "Documentation"
     The documentation is still work in progress.