Error when using scalar vs. vector to operate on tracked inupt about reversediff.jl HOT 1 OPEN

function mwe(a,c)
  # d = @. a/(a + c) # this doesn't work
  # d = @. 1.0/(a + c) # even this doesn't work 
  # d = @. a + c # but this works 
  # d = @. 1.0/a # this also works 
  # but below works 
  d = similar(a)
  @simd for i in eachindex(a)
    @inbounds d[i] = a[i]/(a[i] + c)
  end
  e = map(a,d) do aa, dd
        aa*dd
  end
  return sum(e)
end

a = rand(Normal(),5)
c = 50.0

mwe(a,c)

ReverseDiff.hessian(x -> mwe(x, c), a) 
# works! (haven't checked the correctness, but structure of the matrix is alright.)

function mwe(a,c)
  # d = @. a/(a + c) # doesn't work
  
  # works 
  d = similar(a)
  @. d = a/(a + c)
  
  e = map(a,d) do aa, dd
        aa*dd
  end
  return sum(e)
end

a = rand(Normal(),5)
c = 50.0

mwe(a,c)

ReverseDiff.hessian(x -> mwe(x, c), a)