inversion without regularization

[lheagy]

Right now, the base inverse problem requires that we instantiate it with a regularization. However, if you are running a parametric inversion, regularization might not be necessary. We can hack around this by still creating a regularization but then setting beta to zero. It would be cleaner to remove this as a necessary step and allow regularization to be None.

[ghwilliams]

Looks like one of those issues that end up in the silent and peaceful realm of forgotten issues :). I can think of some possibilities, a major concern is compatibility with already written client codes and the possibility of introducing bugs. One idea would be:

• Create a "DoNothing" regularization class which would simply return zero where appropriate
• Make the parameter "reg" of BaseInvProblem default to this "DoNothing" regularization class. This alternative would be compatible with existing code and do not require touching other parts of the code looking for the possibility of "reg" having the value "None". Does it make sense @lheagy !!?