Frequently Commited Errors by new users.

[proyan]

I have been dealing with certain bugs that are frequently being committed by new users around me. Here I'll try to make a list of those. I will keep editing this issue to add new questions/bugs as they arrive. If you feel there is certain bug that happens frequently in crocoddyl, please don't hesitate to add it here.

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1)[shootingProblem]: Default timeStep in terminalModel, for an integrator.

IntegratedActionModelEuler has a default time of 1e-3. So users are creating runningModels without specifying the time, and in the same vein, terminalModel without specifying the time (since it is a default in the constructor). However, terminalModel needs the time to be zero in the formulation they have in mind.

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2)[shootingProblem]: Default timeStep=0 in runningModel for an integrator.

In crocoddyl API, setting timeStep=0 automatically assumes that the model is a terminalModel. The user intent is to do an integration with dt=0, however, what happens is that integration is disabled.

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3)[shootingProblem]: runningModels contains pointers to the same memory.

Very often in python, and sometimes in c++ as well, user creates an ActionModel, and creates a shootingproblem like this:

model = crocoddyl.SomeActionModel()
problem = crocoddyl.ShootingProblem(init_state, [model]*T, model)

What is expected is that the list runningModels inside the shootingProblem would contain different memories, and changing problem.runningModels[0] would not affect problem.runningModels[1]. What is actually happening is that the same pointer is being copied, and changing any one model changes all models.

Same issue in c++, where new users don't realise that very often what they are providing to the shootingProblem is not a list of ActionModels, but a list of pointers pointing to the same memory location containing an ActionModel.

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4) math behind activationModels, costModels .

There is no cheat-sheet that we can refer to quickly see which function implements what mathematical formula.

[cmastalli]

Hi @proyan

Thanks for collecting some of the common errors made by users.
I believe an issue is not the right place for reporting them.
I would suggest to create a page in the wiki dedicated to these points.
Some points could be also included here: https://github.com/loco-3d/crocoddyl/wiki/Frequently-Asked-Questions.

Said that, I think we could avoid 1 by removing the default value of dt, what do you think?