Add function to return vector_field of continuous system

[ueliwechsler]

Closes #160.

• Adds method vector_field to systems of type AbstractContinuousSystem.
• Rewrites successor method to make it more generic (no need to add a new method for every new type)
• add getter function mapping for retrieving the parametric function:p or blackbox function :f. (function name is WIP though)
• add isblackbox trait
• add Tests and docstring for VectorField type

[mforets]

Is this still WIP?

[ueliwechsler]

Sorry, I did not have that much time to work on this PR in the last weeks.

The only thing that is left to do is the following:

• add Tests and docstring for VectorField type
• Export VectorField and evaluate?

I am not really used to the wording of continuous systems and, to be honest, wording in general 😅. If you could provide some help, that would be really great.

But apart from adding documentation to the VectorField part here

MathematicalSystems.jl/src/instantiate.jl

Lines 215 to 237 in 74745b4

	struct VectorField{T}
	field::T
	end
	# function-like evaluation
	@inline function (V::VectorField)(args...)
	evaluate(V, args...)
	end
	function evaluate(V::VectorField, args...)
	return V.field(args...)
	end
	function VectorField(sys::AbstractContinuousSystem)
	if inputdim(sys) == 0 && noisedim(sys) == 0
	field = (x) -> vector_field(sys, x)
	elseif inputdim(sys) == 0 || noisedim(sys) == 0
	field = (x, u) -> vector_field(sys, x, u)
	else
	field = (x, u, w) -> vector_field(sys, x, u, w)
	end
	return VectorField(field)
	end

and possibly adding a Test for VectorField this PR is fine. And should not be WIP.

[mforets]

Alright, thanks for the write-up. I'm enthusiastic about this PR as it gives access to vector_field. I'll think about naming suggestions and reply back.

[ueliwechsler]

Finally, I finished my work on vector_field and successor rewriting.

[schillic]

Can you split up the file src/instantiate.jl? At least I would not look for successor or VectorField in there. If there is something in common for all the content, a different name would be better.

[ueliwechsler]

Sure. I can create a file vector_field.jl and successor.jl for the corresponding code and keep the _instantiate "helper" methods in the isntantiate.jl file. I could move these three files into folder too. Any good namesuggestions?

[schillic]

Sounds good. I do not have suggestions for a folder name, but I also think we do not need a folder.

[mforets]

lgtm, thanks!

[schillic]

Thanks!
The VectorField struct is not tested I think.

[ueliwechsler]

I added the tests. Should be fine now.

[ueliwechsler]

I haven't done this in a while. Can I just merge or do I have to rebase or similar?
I just remember, that the last time I tried, it ended for me in confusion and chaos😅.

[schillic]

Let's wait if @blegat has something to say. If you have the rights to do so, you can just merge (no conflict here).

[mforets]

Merging!