Hi all,

I have a question about a method error in ReverseDiff.jl, which arises in my function when calling `*`

(line `p/g + p*(a-am)`

in my MWE below), and using ReverseDiff to calculate the Hessian matrix. I’ve checked that ForwardDiff works correctly for this problem (and using ReverseDiff to get just the gradient works too FWIW). I’d really appreciate some help interpreting more details behind the error and any suggestions for how I can fix it.

My deliberately simplified MWE is below. Thanks everyone.

[EDIT]: I’m on Julia 1.8.3 at the latest versions of those package (from the general julia repo).

```
using ForwardDiff
using ReverseDiff
using Distributions
log_ω::Float64 = -4.0
μg = -0.2
log_σg = log(0.1)
μp = 0.2
log_σp = log(0.1)
n = 10
a::Vector{Int64} = rand(Poisson(10), n)
log_g::Vector{Float64} = rand(Normal(μg, exp(log_σg)), n)
log_p::Vector{Float64} = rand(Normal(μp, exp(log_σp)), n)
function mwe(log_ω, log_g, log_p, a)
ω = exp(log_ω)
p = exp.(log_p)
g = exp.(log_g)
am = @. log(p/(g*ω))/g
μ = map(a, am, g, p) do a, am, g, p
if a < am
ω * exp(g*a)
else
p/g + p*(a-am)
end
end
return sum(μ)
end
ForwardDiff.hessian(x -> mwe(log_ω, log_g, x, a), log_p)
ReverseDiff.hessian(x -> mwe(log_ω, log_g, x, a), log_p)
# just the gradients work fine
ForwardDiff.gradient(x -> mwe(log_ω, log_g, x, a), log_p)
ReverseDiff.gradient(x -> mwe(log_ω, log_g, x, a), log_p)
```