add warning for eta0 == 0.0 in BBM equation

Author: JoshuaLampert

docs/src/dispersion.md

@@ -117,7 +117,7 @@ anim = @animate for step in eachindex(sol.u)
     index = argmin(abs.(DispersiveShallowWater.grid(semi) .- x_t_sk))
     scatter([x_t_euler], [initial_condition_traveling_wave(x_t_euler, t, euler, mesh)],
             color = :blue, label = nothing)
-    eta, _ = sol.u[step].x
+    eta, = sol.u[step].x
     scatter!([x_t_sk], [eta[index]],
              color = :green, label = nothing)
     plot!(semi => sol, plot_initial = true, plot_bathymetry = false,

src/dispersion_relation.jl

@@ -69,7 +69,6 @@ function (disp_rel::LinearDispersionRelation)(equations::EulerEquations1D, k)
     return sqrt(g * k * tanh(h0 * k))
 end
 
-# TODO: Factor of 5/2 in front?
 function (disp_rel::LinearDispersionRelation)(equations::BBMEquation1D, k)
     h0 = disp_rel.ref_height
     g = gravity_constant(equations)

src/equations/bbm_1d.jl

@@ -49,6 +49,7 @@ struct BBMEquation1D{RealT <: Real} <: AbstractBBMEquation{1, 1}
 end
 
 function BBMEquation1D(; gravity_constant, D = 1.0, eta0 = 0.0, split_form = true)
+    eta0 == 0.0 || @warn "The still-water surface needs to be 0 for the BBM equations"
     BBMEquation1D(gravity_constant, D, eta0, split_form)
 end