Weird interactions with Unitful

[danielmatz]

I have been trying to use Rotations and Unitful together. At first, it seems like it works well:

julia> RotX(1.0u"°")
3×3 RotX{Unitful.Quantity{Float64,Unitful.Dimensions{()},Unitful.FreeUnits{(Unitful.Unit{:Degree,Unitful.Dimensions{()}}(0, 1//1),),Unitful.Dimensions{()}}}}(1.0°):
 1.0  0.0         0.0      
 0.0  0.999848   -0.0174524
 0.0  0.0174524   0.999848

But then I found that the units propagate incorrectly:

julia> RotX(1.0u"°") * [0, 0, 1]
3-element StaticArrays.SArray{Tuple{3},Unitful.Quantity{Float64,Unitful.Dimensions{()},Unitful.FreeUnits{(Unitful.Unit{:Degree,Unitful.Dimensions{()}}(0, 1//1),),Unitful.Dimensions{()}}},1,3}:
       0.0°
 -0.999949°
   57.2871°

[andyferris]

I guess we are assuming sin(::T) -> T here. We'd need more type-parameters to handle this (one for the AbstractArray's eltype, and one for the stored quantity).

Actually this bug is more widespread than just Unitful integration:

julia> r = RotX(1)
3×3 RotX{Int64}(1):
 1.0  0.0        0.0     
 0.0  0.540302  -0.841471
 0.0  0.841471   0.540302

julia> eltype(r)
Int64

julia> r * [1,1,1]
ERROR: InexactError()
Stacktrace:
 [1] convert(::Type{Int64}, ::Float64) at ./float.jl:679
 [2] macro expansion at /home/ferris/.julia/v0.6/StaticArrays/src/util.jl:11 [inlined]
 [3] convert_ntuple at /home/ferris/.julia/v0.6/StaticArrays/src/util.jl:8 [inlined]
 [4] Type at /home/ferris/.julia/v0.6/StaticArrays/src/SArray.jl:28 [inlined]
 [5] macro expansion at /home/ferris/.julia/v0.6/StaticArrays/src/matrix_multiply.jl:69 [inlined]
 [6] _mul at /home/ferris/.julia/v0.6/StaticArrays/src/matrix_multiply.jl:57 [inlined]
 [7] *(::Rotations.RotX{Int64}, ::Array{Int64,1}) at /home/ferris/.julia/v0.6/StaticArrays/src/matrix_multiply.jl:38

This is lying about an AbstractArray interface function (eltype) and is leading to bad results. :(

[OliverEvans96]

I'm finding that it works as expected for 3D rotations

julia> rx = RotX(38°)
3×3 RotX{Float64} with indices SOneTo(3)×SOneTo(3)(0.663225):
 1.0  0.0        0.0
 0.0  0.788011  -0.615661
 0.0  0.615661   0.788011

julia> rx * [1.0, 2.0, 3.0]
3-element StaticArrays.SVector{3, Float64} with indices SOneTo(3):
  1.0
 -0.27096291876353107
  3.595355211471482

julia> rz = RotZ(38°)
3×3 RotZ{Float64} with indices SOneTo(3)×SOneTo(3)(0.663225):
 0.788011  -0.615661  0.0
 0.615661   0.788011  0.0
 0.0        0.0       1.0

julia> rz * [1.0, 2.0, 3.0]
3-element StaticArrays.SVector{3, Float64} with indices SOneTo(3):
 -0.4433121970445947
  2.191682982539102
  3.0

But appends an extraneous unit in 2D

julia> r2 = Angle2d(38°)
2×2 Angle2d{Quantity{Int64, NoDims, FreeUnits{(°,), NoDims, nothing}}} with indices SOneTo(2)×SOneTo(2)(38°):
 0.788011  -0.615661
 0.615661   0.788011

julia> r2 * [1.0, 2.0]
2-element StaticArrays.SVector{2, Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}} with indices SOneTo(2):
 -25.399917897327196°
  125.57418493013506°

This is with:

• Julia v1.6.0-beta1
• Rotations v1.0.2
• Unitful v1.6.0