Adds methods to mask_immersed_field! for BinaryOperations

[jagoosw]

As discussed in #3676, this PR attempts to add methods to mask_immersed_field! for BinaryOperations so they can be passed as auxiliary fields.

This works for binary operations which combine fields or a field and a number. To make + and - work I have to set the value to -/+ the number value for the field.

[glwagner]

Well done.

[jagoosw]

I think the only place this will fail is for number ^ field since we can never make this zero. We could do:

b_value = ifelse(a < 0, Inf, -Inf)

but this also fails in the case of a==1, although that would be a bit of a strange operation to have written?

[glwagner]

Is it actually important to support the operation ^?

[glwagner]

You don't need to use ifelse here by the way, if is ok. This is not inside a kernel.

[glwagner]

Note that the masking operation is really supposed to set the field to some prescribed value. Not always "0". So it's going to be challenge to cover all cases it would seem.

Do we have to support operations that involve numbers and fields? We could just support fields with fields. Things are easier.

Also there is a problem if a field appears "on its own", and also in a binary operation. Then one masking operation could cancel the other for operations like / and ^. Seems like a bit of a rabbit hole. We could just support + and - and call it good.

[jagoosw]

I think it would be a lot more straight forward to support just + and - and we can guarantee the value is correct then too

[glwagner]

I think it would be a lot more straight forward to support just + and - and we can guarantee the value is correct then too

Ok, let's do that