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Deprecate generic stride implementation (#17812), allow AbstractArrays to use BLAS/LAPACK routines (#25247) #25321

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merged 16 commits into from
Jan 5, 2018
Merged

Deprecate generic stride implementation (#17812), allow AbstractArrays to use BLAS/LAPACK routines (#25247) #25321

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5c5d369
deprecate stride, support AbstractArray in blas routines
Dec 27, 2017
13eb90f
move size_to_strides back to abstractarray.jl
dlfivefifty Dec 28, 2017
acaf1c2
use parents stride in substrides
dlfivefifty Dec 28, 2017
93998ad
Add strides for StridedReshapedArray
dlfivefifty Dec 28, 2017
0858576
Move stride, stride1 to dense.jl
dlfivefifty Dec 29, 2017
903c42e
move strides tests to test/dense.jl
dlfivefifty Dec 29, 2017
4c2885d
_cumsumprodsizes -> _defaultstride, addresses stevengl comments
dlfivefifty Dec 29, 2017
d353ab0
Remove _defaultstride since it's only used one place
dlfivefifty Dec 30, 2017
31d4ce6
Remove restriction to StridedArray in LAPACK
dlfivefifty Dec 30, 2017
9c8fb44
Make strides(A) the default override, make sterner warning in depreca…
dlfivefifty Dec 30, 2017
d1086e0
O(N) substrides implementation
dlfivefifty Dec 30, 2017
579ceec
Deprecate old substrides
dlfivefifty Dec 31, 2017
337785d
work around type inference failure in substrides
dlfivefifty Jan 2, 2018
a558d76
state argument type in substrides so inference is correct
dlfivefifty Jan 4, 2018
7ce3036
merge master
dlfivefifty Jan 4, 2018
346605b
test_deprecated for strides before implementing
dlfivefifty Jan 4, 2018
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4 changes: 2 additions & 2 deletions base/abstractarray.jl
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Expand Up @@ -251,8 +251,8 @@ julia> strides(A)
"""
function strides end

# the definition of strides for Array is the cumsum of the product of sizes
function _cumsumprodsizes(a::AbstractArray, i)
# the definition of strides for Array is cumprod([1;collect(size(A))[1:end-1]])
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well, technically cumprod would return an array, whereas strides returns a tuple

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Hmm, that's not quite right since:

julia> A = Array{Float64,0}()
0-dimensional Array{Float64,0}:
0.0

julia> strides(A)
()

How about saying:

the defition of strides for Array{T,N} is tuple() if N = 0, otherwise it is a tuple containing 1 and a cumulative product of the first N-1 sizes

function _defaultstride(a::AbstractArray, i)
if i > ndims(a)
return length(a)
end
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2 changes: 1 addition & 1 deletion base/linalg/dense.jl
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Expand Up @@ -112,7 +112,7 @@ true
isposdef(A::AbstractMatrix) = ishermitian(A) && isposdef(cholfact(Hermitian(A)))
isposdef(x::Number) = imag(x)==0 && real(x) > 0

stride(A::Union{DenseArray,StridedReshapedArray,StridedReinterpretArray}, i::Int) = Base._cumsumprodsizes(A, i)
stride(A::Union{DenseArray,StridedReshapedArray,StridedReinterpretArray}, i::Int) = Base._defaultstride(A, i)
strides(A::Union{DenseArray,StridedReshapedArray,StridedReinterpretArray}) = size_to_strides(1, size(A)...)

function norm(x::StridedVector{T}, rx::Union{UnitRange{TI},AbstractRange{TI}}) where {T<:BlasFloat,TI<:Integer}
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6 changes: 3 additions & 3 deletions doc/src/manual/interfaces.md
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Expand Up @@ -399,12 +399,12 @@ perhaps range-types `Ind` of your own design. For more information, see [Arrays
| `Base.unsafe_convert(::Type{Ptr{T}}, A)` |   | Return the native address of an array. |


A strided array is a sub-type of `AbstractArray` whose entries are stored in memory with fixed strides.
A strided array is a subtype of `AbstractArray` whose entries are stored in memory with fixed strides.
Provided the element type of the array is compatible with BLAS, a strided array can utilize BLAS and LAPACK routines
for more efficient linear algebra routines.

A typical example of a user defined strided array is one that wraps a standard `Array`
with additional structure.
A typical example of a user-defined strided array is one that wraps a standard `Array`
with additional structure.


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I'd add a warning here too about how dangerous it is to implement these methods if the underlying storage is not actually strided. Otherwise the following might happen:

  • user calls a function. Gets a MethodError due to missing implementation of strides
  • "helpfully" implements strides to fix the method error

It might be useful to give some concrete examples of arrays and categorize them as to whether they have strided memory representation. Examples:

1:5   # not strided (there is no storage associated with this array, could segfault if implemented `strides`)
collect(1:5)  # is strided
A = [1 5; 2 6; 3 7; 4 8]  # is strided
V = view(A, 1:2, :)   # is strided
V = view(A, 1:2:4, :)   # is strided
V = view(A, [1,2,4], :)   # is not strided


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