Advection in Fourier space broken

[vpuri3]

https://github.com/vpuri3/PDEInterfaces.jl/blob/940aee9cf3decda3583c03c6fbcfeff649daaaae/src/Spaces/TrigonometricPolynomials/Fourier.jl#L333-L367

product is being formed in modal space. not real space. i think the way to do this is to write a FunctionOperator:

function advect(duh, uh, p, t)
    # get vh from p
    v <- F \ Xh  * vh
    u <- F \ Xh * Dh * uh
    duh <- F \ (v * u)
end

[vpuri3]

would have to fix SciML/SciMLOperators.jl#56

[vpuri3]

or just figure out how to do adjoints, dealasing correctly by learning fourier methods properly