[Insight-users] Regular Step Gradient Descent optimizer

[Tom Vercauteren]

Hi all,

Thanks for all the nice optimizers in ITK! Here's a small feature
request that IMHO could make many of them easier to use.

As mentioned in this thread, it is possible for several optimizers in
ITK not to optimize the metric value at each step. Hence the last
position might not be the best position visited by the optimizer.

The "disturbing" thing is that the optimizers (and registration
methods) only allow to directly query for the last position (using
optimizer->GetCurrentPosition() or
registration->GetLastTransformParameters() ).

I know it is possible to keep the best position by using observers,
but it would be nice if the optimizers could keep this best position
and if we could simply call something like
optimizer->GetBestPosition() or
registration->->GetBestTransformParameters().

Of course some optimizers (e.g. Powell, LBFGS, FRPR etc.) do not need
to store this position as they can only optimize the metric value. In
such a case GetBestPosition() could simply call GetCurrentPosition().

Regards,
Tom