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Rewrite spdiagm with pairs #23757

Merged
merged 1 commit into from
Oct 11, 2017
Merged

Rewrite spdiagm with pairs #23757

merged 1 commit into from
Oct 11, 2017

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fredrikekre
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@fredrikekre fredrikekre commented Sep 18, 2017

I think this is nicer than the previous spdiagm(tuple_of_vectors, tuple_of_diags) API. And the same should also be implemented for diagm. See #23320 and specifically #23320 (comment)

This also deals with #23320 (comment) such that we always return a square matrix.

Some things to decide:

  • Should the pair be vector => diagonal or diagonal => vector? I think vector => diagonal is nicer.
  • Should we have a convenience constructor for the single vector case? spdiagm(v::AbstractVector) = spdiagm(0 => v). I imagine that case being quite common and it might be nice to have that?

Still need to implement proper deprecations and such.

@fredrikekre
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Actually, the single vector case could better be written as sparse(Diagonal(v)), that should also be faster.

@fredrikekre
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Here are some datapoints that support the changes here, specifically the removal of the option to supply m, n as the final size. In all registered packages there are ≈120 uses of spdiagm as follows:

  • 69 % are simply spdiagm(x::AbstractVector)
  • 21 % are calls to spdiagm(x::AbstractVector, k, m, n) where m, n are needed to obtain a square matrix.
    julia> spdiagm(rand(2), -1)
    3×2 SparseMatrixCSC{Float64,Int64} with 2 stored entries:
      [2, 1]  =  0.0960447
      [3, 2]  =  0.190498
    
    julia> spdiagm(rand(2), -1, 3, 3) # 3, 3 needed to obtain a square matrix
    3×3 SparseMatrixCSC{Float64,Int64} with 2 stored entries:
      [2, 1]  =  0.64661
      [3, 2]  =  0.119494
    
  • 5.9% are calls with multiple diagonals that will be unaffected of the removal of m, n arguments
  • 4.2 % are calls where m != n, e.g. requesting a non-square matrix.

@deprecate spdiagm(x::AbstractVector) sparse(Diagonal(x))
@deprecate spdiagm(x::AbstractVector, d::Number) spdiagm(x => d)
@deprecate spdiagm(x, d) spdiagm((x[i] => d[i] for i in 1:length(x))...)
@deprecate spdiagm(x, d, m::Integer, n::Integer) spdiagm((x[i] => d[i] for i in 1:length(x))...)
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IIUC, the latter now always yields a square matrix whereas the former yields an m-by-n matrix?

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Yea. I should rewrite these deprecations such that this change won't be breaking.

i += numel
end

return (I,J,V)
return I, J, V
end
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The former descriptive variable names made this code a bit easier to follow :).

one diagonal, `B` can be a vector (instead of a tuple) and `d` can be the diagonal position
(instead of a tuple), defaulting to 0 (diagonal). Optionally, `m` and `n` specify the size
of the resulting sparse matrix.
Construct a sparse diagonal matrix from pairs of vectors and diagonals.
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"pairs" -> "Pairs"?

@ViralBShah
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ViralBShah commented Oct 1, 2017

Off topic, I also wish there was a better way to name this and similar functions. It is really annoying to have the sp prefixes.

@StefanKarpinski
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It is really annoying to have the sp prefixes.

The obvious solution would be something like diagm(SparseMatrixCSC, ...).

@ViralBShah
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diagm(SparseMatrixCSC, ...) is what I thought of too, but it feels too verbose. One other possibility is using the Sparse module and calling Sparse.diagm.

@fredrikekre
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That's what I proposed in #23320 and also what we should probably do, see #11557 and #16740. There is currently no API to extend for user arrays for this kind of thing, e.g. zeros, ones, rand etc. But this is unrelated to the current PR.

@fredrikekre fredrikekre changed the title [WIP] Rewrite spdiagm with pairs Rewrite spdiagm with pairs Oct 3, 2017
@fredrikekre fredrikekre mentioned this pull request Oct 3, 2017
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@deprecate spdiagm(x::AbstractVector) sparse(Diagonal(x))
function spdiagm(x::AbstractVector, d::Number)
depwarn(string("spdiagm(x::AbstractVector, d::Number) is deprecated, use ",
"spdiagm(x => d) instead, which now return a square matrix. To preserve the old ",
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"return" -> "returns"?

end
function spdiagm(x, d)
depwarn(string("spdiagm((x1, x2, ...), (d1, d2, ...)) is deprecated, use ",
"spdiagm(x1 => d1, x2 => d2, ...) instead, which now return a square matrix. ",
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"return" => "returns"?

end
function spdiagm(x, d, m::Integer, n::Integer)
depwarn(string("spdiagm((x1, x2, ...), (d1, d2, ...), m, n) is deprecated, use ",
"spdiagm(x1 => d1, x2 => d2, ...) instead, which now return a square matrix. ",
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"return" -> "returns"?

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These changes strike me as a step forward, independent of where diagm and friends go eventually. Much thanks for thinking through the design here and in upstream threads @fredrikekre! :)

A minor, subjective point: I find k => v more natural than v => k, particularly with the pairs consistently identified as kv. But I'm sure this impression varies, and practically the difference is likely negligible :).

@fredrikekre
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A minor, subjective point: I find k => v more natural than v => k, particularly with the pairs consistently identified as kv. But I'm sure this impression varies, and practically the difference is likely negligible :).

I read v => k as "assign vector v to diagonal k" which I feel is more natural compared to "assign diagonal k to vector v" for k => v.
The reason it is currently called kv is that I implemented as k => v first and then changed. We should definitely change this to match whatever we decide.

@Sacha0
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Sacha0 commented Oct 7, 2017

Either orientation sounds good on this end :).

@fredrikekre
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Either orientation sounds good on this end :).

I don't particularly care either. Perhaps other people have some opinions?

@mschauer
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mschauer commented Oct 8, 2017

A matrix can be viewed as an association mapping a number (the k in kth diagonal) to a vector (the kth diagonal). In this light, diagm(k =>d) would be more natural.

@martinholters
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Also, the same vector might be used for different diagonals, but not vice versa.

instead of using one tuple with diagonals and one tuple with vectors
@fredrikekre
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Should be ready now. Wanna take another look @Sacha0 ?

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lgtm from a rapid skim of this iteration! :)

@KristofferC KristofferC merged commit 5295feb into master Oct 11, 2017
@KristofferC KristofferC deleted the fe/spdiagm-pair branch October 11, 2017 07:35
@stevengj
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Do we still have to call SparseArrays.spdiagm_internal in order to get a non-square matrix?

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9 participants