I like that you focus on putting the code into InitializeUniformGrid. Do you have a minute to make the bit on "How To Add A Test Problem" explicitly say "Call Initialize Uniform Grid First." Presently the docs go through the details of adding the FieldType array, but I think we should make InitializeUniformGrid a necessary and sufficient part of a new problem type. Not a blocker for this PR.
I can make add some information about calling InitializeUniformGrid. I
agree that it would make sense to have a note about it in the 'How To Add a
New Baryon Field' doc as well as in the 'Adding a new test problem' doc. I
will add a note that while users can in theory reimplement the field
initialization stuff from InitializeUniformGrid in their own code, a call
to InitializeUniformGrid is cleaner and simpler.