Simple code fails

[haavardhvarnes]

I was trying ForwardDiff and found I have this simple function where calculating jacobian fails:
function g(x::Array{Float64,1})
c1_x1mostneg = x[1] .- x[2:end]
c2_x4mostpos = x[[1,2,3,5]] .- x[4]
return [c1_x1mostneg;c2_x4mostpos]
end
dg = x -> ForwardDiff.jacobian(g, x)
dg(randn(5))

with error message:
julia> dg(randn(5))
ERROR: MethodError: no method matching g(::Array{ForwardDiff.Dual{ForwardDiff.Tag{typeof(g),Float64},Float64,5},1})
Closest candidates are:
g(::Array{Float64,1}) at none:2
Stacktrace:
[1] vector_mode_dual_eval(::typeof(g), ::Array{Float64,1}, ::ForwardDiff.JacobianConfig{ForwardDiff.Tag{typeof(g),Float64},Float64,5,Array{ForwardDiff.Dual{ForwardDiff.Tag{typeof(g),Float64},Float64,5},1}}) at /Users/havard/.julia/packages/ForwardDiff/cXTw0/src/apiutils.jl:37
[2] vector_mode_jacobian(::typeof(g), ::Array{Float64,1}, ::ForwardDiff.JacobianConfig{ForwardDiff.Tag{typeof(g),Float64},Float64,5,Array{ForwardDiff.Dual{ForwardDiff.Tag{typeof(g),Float64},Float64,5},1}}) at /Users/havard/.julia/packages/ForwardDiff/cXTw0/src/jacobian.jl:140
[3] jacobian(::Function, ::Array{Float64,1}, ::ForwardDiff.JacobianConfig{ForwardDiff.Tag{typeof(g),Float64},Float64,5,Array{ForwardDiff.Dual{ForwardDiff.Tag{typeof(g),Float64},Float64,5},1}}, ::Val{true}) at /Users/havard/.julia/packages/ForwardDiff/cXTw0/src/jacobian.jl:17
[4] jacobian(::Function, ::Array{Float64,1}, ::ForwardDiff.JacobianConfig{ForwardDiff.Tag{typeof(g),Float64},Float64,5,Array{ForwardDiff.Dual{ForwardDiff.Tag{typeof(g),Float64},Float64,5},1}}) at /Users/havard/.julia/packages/ForwardDiff/cXTw0/src/jacobian.jl:15 (repeats 2 times)
[5] (::var"#82#83")(::Array{Float64,1}) at ./none:1
[6] top-level scope at none:0

What do I misunderstand here?

[andreasnoack]

The error message clearly states what the problem is. Please use discourse.julialang.org for questions like these.