Dear all,

I’m trying to use Symbolics package in order to implement the symbolic computation of the gradient of a function. For instance given `sin(8.0*x1*x2)`

, I want to compute the partial derivative w.r.t. `x1`

. I implemented the following code:

```
using Symbolics
@variables x1, x2
f = sin(8.0 * x1 * x2)
D = Differential(x1)
println(eval(build_function(expand_derivatives(D(f)),x1,x2)))(pi,1/8.0)
```

However I obtain the error

```
ERROR: LoadError: MethodError: no method matching (::var"#15#16")(::Vector{Float64})
Closest candidates are:
(::var"#15#16")(::Any, ::Any) at /Users/mencarelli/.julia/packages/SymbolicUtils/qulQp/src/code.jl:349 (method too new to be called from this world context.)
```

Secondly, I need to implement a loop to compute all the partial derivatives for a function with 20 variables and store them in a variable `gradient`

. How can I do? Thanks for all the suggestions.