Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

fix zeros in hypot and norm #162

Merged
merged 3 commits into from
Aug 25, 2024
Merged

fix zeros in hypot and norm #162

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
bce86ef
fix zeros in hypot and norm
aplavin Jul 30, 2024
aa57078
Update AccessorsLinearAlgebraExt.jl
aplavin Jul 31, 2024
b84e6b2
Update functionlenses.jl
aplavin Jul 31, 2024
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
5 changes: 4 additions & 1 deletion ext/AccessorsLinearAlgebraExt.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,10 @@ import Accessors: set, @set
using LinearAlgebra: norm, normalize, diag, diagind

set(arr, ::typeof(normalize), val) = norm(arr) * val
set(arr, ::typeof(norm), val) = map(Base.Fix2(*, val / norm(arr)), arr) # should we check val is positive?
function set(arr, ::typeof(norm), val)
omul = iszero(val) ? one(norm(arr)) : norm(arr)
map(Base.Fix2(*, val / omul), arr)
end
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

oneunit instead? Or should we error? This seems to break lens laws.

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

What laws does it break?
Setting norm(x) = 0 should always work, including when norm(x) is already zero.

Changed to oneunit, that's correct indeed!

Copy link
Member

@jw3126 jw3126 Jul 31, 2024 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

norm(set([0,0], norm, val)) == val will not hold for nonzero val. So maybe we should error if iszero(norm(arr))? Personally I want to get an error if I try to normalize the zero vector.
OTOH I suspect we have little violations like this in other places as well though. What do you think?

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Oh, that point is unrelated to this PR: here, we are only changing what happens for @set norm(...) = 0. Meanwhile, zero vector + non-zero norm scenario is already present in current Accessors:

julia> set([0,0], norm, 1)
2-element Vector{Float64}:
 NaN
 NaN

There definitely other cases of similar inequalities happening, eg:

julia> angle(set(0, angle, 0.5))
0.0

julia> o = @o filter(isodd, _)
julia> o(set([1,2,3], o, [4,6]))
Int64[]

Btw, this works and conceptually similar to the norm issue:

julia> set(0+0im, abs, 0.5)
0.5 + 0.0im

but is specific to complex values and their sign() being defined even at zero.

We may think about putting a higher priority on strictly following optics laws and not defining "unlawful" optics. But we should also be careful to keep the Accessors flexibility: for example filter() optic above is clearly useful even in cases that break that law. Setting norm of a zero vector is at a boundary imo: maybe throwing an exception is good enough... At least it returns invalid values (NaNs) and not zeros :)

Copy link
Member Author

@aplavin aplavin Aug 25, 2024 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

@jw3126 is the PR fine in the current state? Zero norm input and similar can be discussed separately, here we don't change them at all.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yeah it is fine sry


set(A, ::typeof(diag), val) = @set A[diagind(A)] = val

Expand Down
5 changes: 4 additions & 1 deletion src/functionlenses.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -150,7 +150,10 @@ set(x::AbstractString, f::Base.Fix1{typeof(parse), Type{T}}, y::T) where {T} = s
set(f, ::typeof(inverse), invf) = setinverse(f, invf)

set(obj, ::typeof(Base.splat(atan)), val) = @set Tuple(obj) = hypot(obj...) .* sincos(val)
set(obj, ::typeof(Base.splat(hypot)), val) = map(Base.Fix2(*, val / hypot(obj...)), obj)
function set(obj, ::typeof(Base.splat(hypot)), val)
omul = iszero(val) ? one(hypot(obj...)) : hypot(obj...)
map(Base.Fix2(*, val / omul), obj)
end

################################################################################
##### strings
Expand Down
4 changes: 4 additions & 0 deletions test/test_functionlenses.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -268,7 +268,9 @@ end
@test @set(abs(-2u"m") = 1u"m") === -1u"m"
@test @set(abs(x) = 10) ≈ 6 + 8im
@test @set(angle(x) = π/2) ≈ 5im
@test set(0, abs, 0) == 0
@test set(0, abs, 10) == 10
@test set(0+0im, abs, 0) == 0+0im
@test set(0+0im, abs, 10) == 10
@test set(0+1e-100im, abs, 10) == 10im
@test_throws DomainError @set(abs(x) = -10)
Expand Down Expand Up @@ -300,7 +302,9 @@ end
@test set((3, 4), norm, 10) === (6., 8.)
@test set((a=3, b=4), norm, 10) === (a=6., b=8.)
test_getset_laws(norm, (3, 4), 10, 12)
test_getset_laws(norm, (0, 0), 0, 0)
test_getset_laws(Base.splat(hypot), (3, 4), 10, 12)
test_getset_laws(Base.splat(hypot), (0, 0), 0, 0.)

test_getset_laws(!(@optic _.a), (a=true,), false, true)
test_getset_laws(!(@optic _[1]), (a=true,), false, true)
Expand Down
Loading