Tutorial for (mostly Symbol based) interfacing with problems, integrators, and solutions

[TorkelE]

Add a new tutorial on how to e.g. do sol[:X1] to get solution values of X1. Also mentioned remake and how to do

@unpack X1 = rn

and use X1 instead of :X1.

Makes minor modifications in the callback and plotting description of the advanced simulation tutorial to use this notation.

[TorkelE]

This should be ready for merging, if checks pass.

[isaacsas]

Suggested change

	sol = solve(deepcopy(jprob), SSAStepper(); callback=cb)
	sol = solve(jprob, SSAStepper(); callback=cb)

Why are you using deepcopy? I wouldn't use this in a tutorial as it will just lead to confusion.

[TorkelE]

I though deepcopy was the way to go for complicated structures with other structures within them? Happy to be corrected though.

[isaacsas]

Why are you copying it at all though? You just defined it 11 lines above.

The only reason to deepcopy is if you are going to change something in it and want to keep the original around, but you never use it again so I'm not sure why it being mutated matters?

[TorkelE]

Admittedly this is the last solve of the problem in this example, but assuming hypothetical following code this seems sensible though? Or imagine someone just rerunning that last line 2-3 times to see different solutions.

It feels like good practise to pass a copy of the problem when using mutating callbacks.

[TorkelE]

Admittedly this is the last solve of the problem in this example, but assuming hypothetical following code this seems sensible though? Or imagine someone just rerunning that last line 2-3 times to see different solutions.

It feels like good practise to pass a copy of the problem when using mutating callbacks.

[isaacsas]

Maybe a better example here is to run and plot like 10 solutions. Then you would need to keep the original around as indeed I think you'd have an issue without using deep copies due to the mutation (i.e. the problem would be in an inconsistent state on the next simulation). Then you can use deepcopy, but I'd also add an explanation then for why it is needed.

[isaacsas]

But to be honest, the better approach would be to show users how to then reset things via mutation of the original problem again to have the original values.

[TorkelE]

Wanted to keep the example focused, and not make a full ensemble as that is pretty much a repeat of another tutorial. Will do some more explaining of deepcopy, and link the ensemble example where I actually show why the deepcopy is important.

[TorkelE]

But to be honest, the better approach would be to show users how to then reset things via mutation of the original problem again to have the original values.

How you mean, just reset the value after the simulation has finished?

[TorkelE]

Ok, so this example is proceeded by one where we explain, with examples, why deepcopy is needed (line 185 to 265). I think is is well explained, but tell me if you think there should be further changes.

[isaacsas]

Could you fix the examples that are failing and giving errors when building the docs?

After that feel free to merge -- I can't really read through till mid-next week, and I can just tweak it if I want to update anything at that time.