Limit on `order` in `makefilter` to ensure positivity of the filter in physical space

[glwagner]

@kburns suggests it may be so.

https://github.com/FourierFlows/FourierFlows.jl/blob/0802dc331a549d5d59ab8087b39c4ac5bd97196a/src/domains.jl#L343

[navidcy]

This is a wavenumber filter. When you say "physical space" you mean when you take, e.g., ifft(filter)?

Why does the wavenumber filter have to be positive in physical space...? Am I missing something @glwagner?

[navidcy]

OK, I see.. You are making the point that changing the order can make the filter transition from something like a smooth gaussian filter to a "top-hat" filter in wavenumber space. And this would induce ringing artifacts.