Remove unicode char in keyword arguments (or offer an alternative) ?

[franckgaga]

@baggepinnen
There is a palpable hate against unicode characters, especially in keyword arguments of public functions. Some keyword arguments of this package use them e.g.: σP_0, σQ, σR and x̂_0. I personally like them for the conciseness. It is also well known that σ is a standard deviation, and ^, a modifier for an estimated value. Should we offer an alternative, something like:

function SteadyKalmanFilter(
    model::Linmodel;
    i_ym = 1:model.ny,
    σQ = fill(1/model.nx, model.nx),
    σR = fill(1, length(i_ym)),
    nint_u = 0,
    σQint_u = fill(1, max(sum(nint_u), 0)),
    nint_ym = default_nint(model, i_ym, nint_u),
    σQint_ym = fill(1, max(sum(nint_ym), 0))
    sigmaR = σR,                  # new kwarg 
    sigmaQ = σQ,                  # new kwarg
    sigmaQint_u = σQint_u,        # new kwarg
    sigmaQint_ym = σQint_ym       # new kwarg
)    
    # estimated covariances matrices (variance = σ²) :
    Q̂  = Hermitian(diagm(NT[sigmaQ;  sigmaQint_u;  sigmaQint_ym ].^2), :L)
    R̂  = Hermitian(diagm(NT[sigmaR;].^2), :L)
    return SteadyKalmanFilter{NT, SM}(model, i_ym, nint_u, nint_ym, Q̂ , R̂)
end

and something similar with x̂_0 and xhat_0 ?

[baggepinnen]

I guess it's good practice to have non-unicode API in general. I also like Unicode, but there are certainly cases where it's awkward or hard to type. Most editors can be configured to make it easy, but one might not always be using a computer on which everything has been customized to ones liking.

I was in a previously in a position where I transitioned between multiple different computers in a lab, all running Julia (on different operating systems) to control robots and perform sys.id., and in this context it would have been a hassle to configure everything to work as well as on my main development machine.