Reinterpret 3D array into array of SMatrices

General Usage
1

I don’t understand why I can’t reinterpret a 3D array of float as an array of static matrices. i’m trying to do this:

A = rand(2,3,5)
# can do
julia> reinterpret(SVector{3,Float64},A[1,:,:],(5,))
5-element Array{SVector{3,Float64},1}:
 [0.23546, 0.907289, 0.740175]   
 [0.61008, 0.734986, 0.629369]   
 [0.996311, 0.0236219, 0.452736] 
 [0.926702, 0.754213, 0.0497403] 
 [0.00632655, 0.469851, 0.832494]

# but not
julia> reinterpret(SMatrix{2,3,Float64},A,(5,))
ERROR: ArgumentError: cannot reinterpret Array{Float64} to ::Type{Array{SMatrix{2,3,Float64}}}, type SMatrix{2,3,Float64} is not a bits type

I don’t understand. I want a 5-element Array{SMatrix{2,3,Float64},1}, analog to the first example. I’m coming from FixedSizeArrays (julia v0.5) where this work like

# julia v0.5
julia> using FixedSizeArrays
julia> reinterpret(Mat{2,3,Float64},A,(5,))
5-element Array{FixedSizeArrays.Mat{2,3,Float64},1}:
 FixedSizeArrays.Mat{2,3,Float64}(
    0.5574181712074888 0.9644487115785165 0.6704697319255919
    0.9975096208909706 0.2222225851632973 0.14946990105711122
)
   
 FixedSizeArrays.Mat{2,3,Float64}(
    0.28001812808230175 0.44931736683789114 0.322378156341002
    0.46665857950152345 0.14451919484905318 0.22147629055395557
)

 FixedSizeArrays.Mat{2,3,Float64}(
    0.0002579687549821852 0.8900462296197154 0.5851686490075749
    0.6029813419932457 0.7732024531312345 0.12115694131802379
)

 FixedSizeArrays.Mat{2,3,Float64}(
    0.41651532906948185 0.44625111837501996 0.09088448384005732
    0.8730213366071933 0.7085121876088183 0.2729717970821717
)
 
 FixedSizeArrays.Mat{2,3,Float64}(
    0.3853576197872626 0.13637018253558097 0.04404747821364219
    0.9183888520473955 0.6311436084278026 0.9758791739746058
)
2

You need to specify the last type parameter in the SMatrix which I believe is M*N (easily checked with typeof).

3

dang, that was stupid. thanks!

4

I’m reactivating this thread since this doesn’t seem to work anymore in v0.7, unless I’m misunderstanding the explained solution (very possible). Here’s what I’m trying:

julia> using StaticArrays

julia> A = rand(2,4,5);

julia> reinterpret(SMatrix{2,4,Float64,8},A)
ERROR: ArgumentError:     cannot reinterpret an `Float64` array to `SArray{Tuple{2,4},Float64,2,8}` whose first dimension has size `2`.
    The resulting array would have non-integral first dimension.

Stacktrace:
 [1] (::getfield(Base, Symbol("#thrownonint#190")){Float64,SArray{Tuple{2,4},Float64,2,8}})(::Type{Float64}, ::Type{SArray{Tuple{2,4},Float64,2,8}}, ::Int64) at ./reinterpretarray.jl:24
 [2] reinterpret(::Type{SArray{Tuple{2,4},Float64,2,8}}, ::Array{Float64,3}) at ./reinterpretarray.jl:39
 [3] top-level scope at none:0
5 
julia> using StaticArrays

julia> A = rand(2,4,5);

julia> reinterpret(SMatrix{2,4,Float64,8},reshape(A, length(A)))
5-element reinterpret(SArray{Tuple{2,4},Float64,2,8}, ::Array{Float64,1}):
 [0.17061 0.569503 0.986942 0.623712; 0.381364 0.963277 0.252662 0.504635] 
 [0.595363 0.364473 0.386016 0.122044; 0.901013 0.740808 0.823493 0.933547]
 [0.0286543 0.606252 0.116737 0.921229; 0.27438 0.426807 0.570889 0.186989]
 [0.467349 0.567191 0.288745 0.724425; 0.776126 0.623564 0.490382 0.979833]
 [0.848398 0.485889 0.232903 0.03917; 0.801746 0.0139404 0.422298 0.834867]

Warning: The result may be slow on 1.0. Something that works fast now but is expected to stop working cause very weird bugs in the future is

julia> typ = SMatrix{2,4,Float64,8}
julia> ccall(:jl_reshape_array, Vector{typ}, (Any,Any,Any), Vector{typ}, A, (size(A,3),))
5-element Array{SArray{Tuple{2,4},Float64,2,8},1}:
 [0.17061 0.569503 0.986942 0.623712; 0.381364 0.963277 0.252662 0.504635] 
 [0.595363 0.364473 0.386016 0.122044; 0.901013 0.740808 0.823493 0.933547]
 [0.0286543 0.606252 0.116737 0.921229; 0.27438 0.426807 0.570889 0.186989]
 [0.467349 0.567191 0.288745 0.724425; 0.776126 0.623564 0.490382 0.979833]
 [0.848398 0.485889 0.232903 0.03917; 0.801746 0.0139404 0.422298 0.834867]