Create residual viscosity package +rv and generalize the ResidualViscosity class - Generalize residual viscosity, by passing user-defined flux and calculating the time derivative outside of the update. - Create separate RungekuttaRV specifically using interior RV updates - Separate the artifical dissipation operator from the scheme AdvectionRV1D so that the same scheme can be reused for creating the diff op used by the ResidualViscosity class

function F = semidiscrete2function(D,S)
    % TODO: Find threshhold when sparse makes sense.
    % TODO: Why does having the spase block slow down convergence.m (or does it?)
    if size(D,1) > 500
        D = sparse(D);
    end

    if ~isa(S,'function_handle')
        F = @(w,t)(D*w + S);
    else
        F = @(w,t)(D*w + S(t));
    end
end