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Change broadcast form

I would like to make the following broadcast expression:

J = rand(4,4) fx1 = rand(2,2) fx2 = rand(2,2) @. J[:,1] = fx1 + fx2

I want it very much:

 @. J[:,1] = vec(fx1 + fx2)

where this vec says it should change to 4x1, but I do not want this selection. How could this be handled as a whole (i.e. do not index on fx)?

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arrays julia-lang
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3 answers

Another possibility, instead of vec is for fx1 and fx2 to change fragment J :

 Jcol = reshape(view(J,:,1),(2,2)) @. Jcol = fx1 + fx2

Not sure about the efficiency, but it can give a clearer perspective depending on the surrounding algorithm. The LLVM code seems short enough, and the assignment statement is clear.

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You can free vec from the @. macro @. protecting it with $ :

 julia> expand(:(@. J[:,1] = $vec(fx1) + $vec(fx2))) :((Base.broadcast!)(+, (Base.dotview)(J, :, 1), (vec)(fx1), (vec)(fx2)))
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Since vecs are views, the following works:

 J = rand(4,4) fx1 = rand(2,2) fx2 = rand(2,2) vfx1,vfx2 = vec(fx1),vec(fx2) @. J[:,1] = vfx1 + vfx2

I don’t think there is a way to do this on the same line as I wanted, but that’s fine.

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