mtfishman/stridedviews.jl

A Julia package to represent strided views over a parent DenseArray

StridedViews

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StridedViews.jl exports a single struct type StridedView for representing a strided view over a contiguous parrent array, as represented by the abstract type DenseArray.

See Strided.jl for more functionality.

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The type StridedView provides a view into a parent array of type DenseArray such that the resulting view is strided, i.e. any dimension has an associated stride, such that e.g.

getindex(A, i₁, i₂, i₃, ...) = A.op(A.parent[offset + 1 + (i₁-1)*s₁ + (i₂-1)*s₂ + (i₃-1)*s₃ + ...])

with sⱼ = stride(A, iⱼ). There are no further assumptions on the strides, e.g. they are not assumed to be monotonously increasing or have s₁ == 1. Furthermore, A.op can be any of the operations identity, conj, transpose or adjoint (the latter two are equivalent to the former two if eltype(A) <: Number). Since these operations are their own inverse, they are also used in the corresponding setindex!.

This definition enables a StridedView to be lazy (i.e. returns just another StridedView over the same parent data) under application of conj, transpose, adjoint, permutedims and indexing (getindex) with Union{Integer, Colon, AbstractRange{<:Integer}} (a.k.a slicing). The function sview is exported to directly create a sliced (and thus strided) view over a given parent array.

Furthermore, the strided structure can be retained under certain reshape operations, but not all of them. Any dimension can always be split into smaller dimensions, but two subsequent dimensions i and i+1 can only be joined if stride(A,i+1) == size(A,i)*stride(A,i). Instead of overloading reshape, Strided.jl provides a separate function sreshape which returns a StridedView over the same parent data, or throws a runtime error if this is impossible.