Fix non-vector input Jacobian creation (#128)

* Fix non-vector input Jacobian creation

* Update abstract.jl

Co-authored-by: Patrick Kofod Mogensen <patrick.mogensen@gmail.com>

src/objective_types/abstract.jl

@@ -16,12 +16,8 @@ function make_fdf(x, F::Number, f, g!)
 end
 
 # Initialize an n-by-n Jacobian
-function alloc_DF(x, F)
-  a = (Base.OneTo(length(F)), Base.OneTo(length(x)))
-  df = similar(F, a)
-  fill!(df, NaN)
-  return df
-end
+alloc_DF(x, F) = eltype(x)(NaN) .* vec(F) .* vec(x)'
+
 # Initialize a gradient shaped like x
 alloc_DF(x, F::T) where T<:Number = x_of_nans(x, promote_type(eltype(x), T))
 # Initialize an n-by-n Hessian