f(x::Real) = f(float(x)) leads to stackoverflow

[cossio]

Many definitions follow this pattern:

f(x::AbstractFloat) = 2x # any computation here
f(x::Real) = f(float(x))

But then:

julia> ForwardDiff.derivative(f, 1.)
ERROR: StackOverflowError:
Stacktrace:
 [1] f(::ForwardDiff.Dual{ForwardDiff.Tag{typeof(f),Float64},Float64,1}) at ./REPL[3]:1 (repeats 80000 times)

Because float(Dual) gives Dual which is not AbstractFloat. Is there a way around this?

[cossio]

I did not realize this was being discussed elsewhere

JuliaLang/julia#26552
#261
#324
musm/SLEEF.jl#11

[DilumAluthge]

This is a known limitation of ForwardDiff.jl: http://www.juliadiff.org/ForwardDiff.jl/latest/user/limitations.html The only ways around this that I can think of will come from either Cassette.jl/Capstan.jl or Zygote.jl.

…

On Tue, Oct 9, 2018 at 10:39 Jorge Fernandez-de-Cossio-Diaz < ***@***.***> wrote: Many definitions follow this pattern: f(x::AbstractFloat) = 2x # any computation here f(x::Real) = f(float(x)) But then: julia> ForwardDiff.derivative(f, 1.) ERROR: StackOverflowError: Stacktrace: [1] f(::ForwardDiff.Dual{ForwardDiff.Tag{typeof(f),Float64},Float64,1}) at ./REPL[3]:1 (repeats 80000 times) Because float(Dual) gives Dual which is not AbstractFloat. Is there a way around this? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#366>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFXArUS8XVaEkZPt2UetUbYm21UVFO9Kks5ujLUlgaJpZM4XTcLM> .

[DilumAluthge]

My apologies, I misunderstood your issue. Thanks for posting the correct issue links.

…

On Tue, Oct 9, 2018 at 10:55 Dilum Aluthge ***@***.***> wrote: This is a known limitation of ForwardDiff.jl: http://www.juliadiff.org/ForwardDiff.jl/latest/user/limitations.html The only ways around this that I can think of will come from either Cassette.jl/Capstan.jl or Zygote.jl. On Tue, Oct 9, 2018 at 10:39 Jorge Fernandez-de-Cossio-Diaz < ***@***.***> wrote: > Many definitions follow this pattern: > > f(x::AbstractFloat) = 2x # any computation here > f(x::Real) = f(float(x)) > > But then: > > julia> ForwardDiff.derivative(f, 1.) > ERROR: StackOverflowError: > Stacktrace: > [1] f(::ForwardDiff.Dual{ForwardDiff.Tag{typeof(f),Float64},Float64,1}) at ./REPL[3]:1 (repeats 80000 times) > > Because float(Dual) gives Dual which is not AbstractFloat. Is there a way > around this? > > — > You are receiving this because you are subscribed to this thread. > Reply to this email directly, view it on GitHub > <#366>, or mute the > thread > < https://github.com/notifications/unsubscribe-auth/AFXArUS8XVaEkZPt2UetUbYm21UVFO9Kks5ujLUlgaJpZM4XTcLM > > . > — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#366 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFXArT8IrJTSRDrq7Q51nlNxcmyyIwfdks5ujLi1gaJpZM4XTcLM> .