Suppose I want to extract and operate on only a few components from an SVector, e.g. using StaticArrays f( (x, y, z) ) = (3x, 4y, 5z) v = SVector( (2i for i in 1:10)...) indices = (1, 3, 5) v2 = getindex.(Ref(v), indices) w = f(v2) How do I now put the values from w back into the same positions …

This might be a good use case for Setfield.jl

I could be wrong, but I believe the Setfield solution would produce pretty similar machine code to using an MVector instead and just broadcasting setindex!. In both cases you basically just create copies of tuples with apropriate entries swapped out.

Broadcasting doesn’t work since it returns several copies of the vector. It looks like the solution is just a for loop: using StaticArrays f( (x, y, z) ) = (3x, 4y, 5z) v = SVector( (2i for i in 1:10)...) indices = (1, 3, 5) v2 = getindex.(Ref(v), indices) result = f(v2) for i in 1:length(indi…

Is v there still SVector? or did you go with MVector?

[image] dpsanders: Broadcasting doesn’t work since it returns several copies of the vector. If you do MVector, the initial thing is mutated, so eg this works: f( (x, y, z) ) = (3x, 4y, 5z) v = MVector( (2i for i in 1:10)...) indices = (1, 3, 5) w = f(getindex.(Ref(v), indices)) setindex!.(Re…

[image] marius311: etfield solution would produce pretty similar machine code to using an MVector I have the impression that they are not the same. One is an array of static size that leaves most likely in the heap, while the immutable one will be more agressively optimized. At least my exper…

I think on recent versions of Julia (maybe 1.6?), MVector can be stack allocated as well. E.g.: julia> function foo(x) x[1] = 1 x[2] = 2 x[3] = 3 sum(x) end foo (generic function with 2 methods) julia> x = @MVector[0,0,0]; julia> @allocated foo(x…

[image] marius311: julia> x = @MVector[0,0,0]; For longer vectors, MVector does seem to be much faster, thanks.

[image] SparseMatrix or SArray, MArray? New to Julia For convenience, yes, but this is what I mean: using StaticArrays, BenchmarkTools, Setfield function mut!(A) A .= A .+ 1 end Base.setindex!(m::SMatrix,value,i,j) = @set! m[i,j] = value A1 = rand(3,3) A2 = rand(MMat…

Operate only on a few components of a static vector

General Usage

lmiq June 4, 2021, 11:33pm 11

Look at this. For longer vectors that changes? Is that the point?

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Operate only on a few components of a static vector

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