# DIffEqFlux loss function with variable solve options
**URL:** https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361
**Category:** General Usage
**Tags:** diffeq, zygote, sciml
**Created:** [September 27, 2020, 12:13pm UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361 "2020-09-27T12:13:45Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@FHell](https://discourse.julialang.org/u/FHell)
#### Post date: [September 27, 2020, 12:13pm UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361/1 "2020-09-27T12:13:45Z")
Does someone know a good way to pass solve options to a custom loss function? We are building a package and would like to provide a loss function of the DiffEqFlux type, and I would like the user to be able to control the solver from the outside, e.g. in pseudocode:
```julia
function library_loss(p; solver_options...)
sol = solve(Problem; solver_options...)
end
```
But this does not seem to be compatible with Zygote which complains about named tuples no matter how I try to hide this…
Edit: If needed (e.g. no one has come across this) I will whip up a MWE sometime next week…
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 27, 2020, 12:26pm UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361/2 "2020-09-27T12:26:28Z")
> [@FHell](#):
>
> But this does not seem to be compatible with Zygote which complains about named tuples no matter how I try to hide this…
>
> Edit: If needed (e.g. no one has come across this) I will whip up a MWE sometime next week…
make an MWE. That should be fine? Unless it’s a Zygote bug, but I thought I found all of the Zygote NamedTuple bugs already. Worth getting it documented for @dhairyagandhi96
---
### Author:  [@FHell](https://discourse.julialang.org/u/FHell)
#### Post date: [September 30, 2020, 8:06am UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361/3 "2020-09-30T08:06:13Z")
Thanks Chris for letting me know it should work! The NamedTuple Error was triggered by incorrect behaviour in our code (missing Semicolon), the only surprising part is that the bug doesn’t prevent the normal code to run (as long as no keyword arguments are actually passed):
```nohighlight
using DiffEqFlux
using OrdinaryDiffEq
function l1(p; solver_options...)
dd_spec = solve(ODEProblem((dy,y,p,t) -> dy .= p, zeros(2), (0., 10.), p), Tsit5(), saveat=0.:0.1:10.
, solver_options...) # Comma instead of semicolon here
sum(dd_spec[end])
end
l1(ones(2)) # This works despite the missing semicolon
DiffEqFlux.sciml_train(
l1,
ones(2),
DiffEqFlux.ADAM(0.5),
maxiters = 2) # NamedTuple Error.
# Apparently splatted keyword arguments being passed
# splatted into arguments is not so good (and almost
# certainly this is never going to be the intended behaviour).
# The following works as expected:
function l2(p; solver_options...)
dd_spec = solve(ODEProblem((dy,y,p,t) -> dy .= p, zeros(2), (0., 10.), p), Tsit5(), saveat=0.:0.1:10.; solver_options...)
sum(dd_spec[end])
end
l2(ones(2))
DiffEqFlux.sciml_train(
l2,
ones(2),
DiffEqFlux.ADAM(0.5),
maxiters = 2)
```
While reducing this I also came across the follwoing failure to differentiate. We create a temporary array of arrays, don’t use it, and that throws off the adjoint. Again, this is triggered by having code you don’t want to have in the first place, but that is perfectly valid.
```julia
function l3(p)
ps = [p[1 + (n - 1) * 2:n * 2] for n in 1:10] # This is unused
dd_spec = solve(ODEProblem((dy,y,p,t) -> dy .= p, zeros(2), (0., 10.), p[1:2]), Tsit5())
sum(dd_spec[end])
end
l3(ones(20))
DiffEqFlux.sciml_train(
l3,
ones(20),
DiffEqFlux.ADAM(0.5),
maxiters = 2) # MethodError: no method matching iterate(::Nothing)
```
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 30, 2020, 1:34pm UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361/4 "2020-09-30T13:34:46Z")
Yeah, open an issue on Zygote for that. @dhairyagandhi96 should take notice. But what you’re pointing out are all Zygote behaviors and not DiffEqFlux specifically.
---
### Author:  [@dhairyagandhi96](https://discourse.julialang.org/u/dhairyagandhi96)
#### Post date: [September 30, 2020, 2:04pm UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361/5 "2020-09-30T14:04:11Z")
Hmm, we did fix a bug with the kwargs handling some time back, if so could you please MWE something like
```julia
julia> f(x; kwargs...) = 2x .+ kwargs[1]
f (generic function with 1 method)
julia> f(5, b = true)
11
julia> gradient(x -> f(x, b = true), 40)
(2,)
```
Could you share the specific named tuples error you saw?
---
### Author:  [@dhairyagandhi96](https://discourse.julialang.org/u/dhairyagandhi96)
#### Post date: [September 30, 2020, 2:09pm UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361/6 "2020-09-30T14:09:49Z")
For the other error, an mwe like so might be it
```julia
julia> function g(x)
# p = zeros(size(x))
p = [2i for i in x]
sum(x)
end
g (generic function with 2 methods)
julia> gradient(g, rand(3,3))
ERROR: MethodError: no method matching iterate(::Nothing)
Closest candidates are:
iterate(::DataStructures.SparseIntSet, ::Any...) at /home/dhairyalgandhi/.julia/packages/DataStructures/mgePl/src/sparse_int_set
.jl:147
iterate(::Base.RegexMatchIterator) at regex.jl:552
iterate(::Base.RegexMatchIterator, ::Any) at regex.jl:552
...
```
---
### Author:  [@FHell](https://discourse.julialang.org/u/FHell)
#### Post date: [October 3, 2020, 6:42am UTC](https://discourse.julialang.org/t/diffeqflux-loss-function-with-variable-solve-options/47361/7 "2020-10-03T06:42:02Z")
Yeah, that’s it. I posted a MWE for the first error here:
[https://github.com/FluxML/Zygote.jl/issues/803](https://github.com/FluxML/Zygote.jl/issues/803)
Edit: And the other is here:
[https://github.com/FluxML/Zygote.jl/issues/804](https://github.com/FluxML/Zygote.jl/issues/804)