Clarify variable names in some docstrings

docs/src/callbacks.md

@@ -77,10 +77,12 @@ nothing # hide
 
 The analysis callback computes ``L^2`` and ``L^\infty`` errors by comparing the numerical solution to the initial condition at time ``t`` (which can be the analytical solution, if available). Additional error types can be specified using the `extra_analysis_errors` parameter, and physical quantities can be monitored using `extra_analysis_integrals`.
 
-The conservation error measures the temporal change of conserved quantities. For the BBM-BBM equations, important conserved quantities include the total water mass (integral of water height `h`), the total momentum (integral of `v` for flat bathymetry), and the total [`entropy`](@ref). The specific form of the entropy varies between different equation systems. For the BBM-BBM equations, the integral of the entropy is:
+The conservation error measures the temporal change of conserved quantities. For the BBM-BBM equations, important conserved quantities include the total water mass (integral of water height `h` given
+by [`waterheight_total`](@ref)), the total momentum (integral of `v` for flat bathymetry given by [`velocity`](@ref)), and the total entropy (integral of `U` given by [`entropy`](@ref)). The specific
+form of the [`entropy`](@ref) varies between different equation systems. For the BBM-BBM equations, the integral of the entropy is:
 
 ```math
-\mathcal E(t; \eta, v) = \frac{1}{2}\int_\Omega g\eta^2 + (\eta + D)v^2 \, dx
+\mathcal E(t; \eta, v) = \int_\Omega U(\eta, v) \, dx = \frac{1}{2}\int_\Omega g\eta^2 + (\eta + D)v^2 \, dx
 ```
 
 where ``\eta`` is the total water height and ``D`` is the still-water depth.

src/equations/bbm_1d.jl

@@ -22,12 +22,12 @@ for `split_form = true` and in Linders, Ranocha, and Birken (2023) for `split_fo
 If `split_form` is `true`, a split form in the semidiscretization is used, which conserves
 - the total water mass (integral of ``h``) as a linear invariant
 - a quadratic invariant (integral of ``1/2\eta(\eta - 1/6D^2\eta_{xx})`` or for periodic boundary conditions
-  equivalently ``1/2(\eta^2 + 1/6D^2\eta_x^2)``), which is called here [`energy_total_modified`](@ref)
+  equivalently ``\hat U = 1/2(\eta^2 + 1/6D^2\eta_x^2)``), which is called here [`energy_total_modified`](@ref)
   (and [`entropy_modified`](@ref)) because it contains derivatives of the solution
 
 for periodic boundary conditions. If `split_form` is `false` the semidiscretization conserves
 - the total water mass (integral of ``h``) as a linear invariant
-- the Hamiltonian (integral of ``1/4\sqrt{g/D}\eta^3 + 1/2\sqrt{gD}\eta^2``) (see [`hamiltonian`](@ref))
+- the Hamiltonian (integral of ``H = 1/4\sqrt{g/D}\eta^3 + 1/2\sqrt{gD}\eta^2``) (see [`hamiltonian`](@ref))
 
 for periodic boundary conditions.
 
@@ -195,23 +195,23 @@ function rhs!(dq, q, t, mesh, equations::BBMEquation1D, initial_condition,
 end
 
 """
-    energy_total_modified!(e, q_global, equations::BBMEquation1D, cache)
+    energy_total_modified!(e_mod, q_global, equations::BBMEquation1D, cache)
 
-Return the modified total energy `e` of the primitive variables `q_global` for the
+Return the modified total energy ``\\hat e`` of the primitive variables `q_global` for the
 [`BBMEquation1D`](@ref). The `energy_total_modified`
 is a conserved quantity (for periodic boundary conditions).
 
 It is given by
 ```math
-\\frac{1}{2} \\eta(\\eta - \\frac{1}{6}D^2\\eta_{xx}).
+\\hat e(\\eta) = \\frac{1}{2} \\eta(\\eta - \\frac{1}{6}D^2\\eta_{xx}).
 ```
 
 `q_global` is a vector of the primitive variables at ALL nodes.
 `cache` needs to hold the SBP operators used by the `solver`.
 
 See also [`energy_total_modified`](@ref).
 """
-function energy_total_modified!(e, q_global, equations::BBMEquation1D, cache)
+function energy_total_modified!(e_mod, q_global, equations::BBMEquation1D, cache)
     eta, = q_global.x
     D = equations.D
 
@@ -223,17 +223,17 @@ function energy_total_modified!(e, q_global, equations::BBMEquation1D, cache)
         mul!(eta_xx, D2, eta)
     end
 
-    @.. e = 0.5 * eta * (eta - 1 / 6 * D^2 * eta_xx)
-    return e
+    @.. e_mod = 0.5 * eta * (eta - 1 / 6 * D^2 * eta_xx)
+    return e_mod
 end
 
 """
     hamiltonian!(H, q_global, equations::BBMEquation1D, cache)
 
-Return the Hamiltonian `H` of the primitive variables `q_global` for the
+Return the Hamiltonian ``H`` of the primitive variables `q_global` for the
 [`BBMEquation1D`](@ref). The Hamiltonian is given by
 ```math
-\\frac{1}{4}\\sqrt{\\frac{g}{D}}\\eta^3 + \\frac{1}{2}\\sqrt{gD}\\eta^2.
+H(\\eta) = \\frac{1}{4}\\sqrt{\\frac{g}{D}}\\eta^3 + \\frac{1}{2}\\sqrt{gD}\\eta^2.
 ```
 
 `q_global` is a vector of the primitive variables at ALL nodes.

src/equations/bbm_bbm_1d.jl

@@ -32,12 +32,12 @@ Ranocha et al. (2020) and generalized for a variable bathymetry in
 Lampert and Ranocha (2025). It conserves
 - the total water mass (integral of ``h``) as a linear invariant
 - the total velocity (integral of ``v``) as a linear invariant for flat bathymetry
-- the total energy
+- the total entropy/energy (integral of ``U = 1/2 hv^2 + 1/2 g\eta^2``)
 
 for periodic boundary conditions (see Lampert, Ranocha). For reflecting boundary conditions,
 the semidiscretization conserves
 - the total water (integral of ``h``) as a linear invariant
-- the total energy.
+- the total entropy/energy (integral of ``U = 1/2 hv^2 + 1/2 g\eta^2``)
 
 Additionally, it is well-balanced for the lake-at-rest stationary solution, see Lampert and Ranocha (2025).
 
@@ -412,7 +412,7 @@ end
 # Discretization that conserves
 # - the total water (integral of ``h``) as a linear invariant
 # - the total momentum (integral of ``v``) as a linear invariant for flat bathymetry
-# - the total energy
+# - the total entropy/energy (integral of ``U = 1/2 hv^2 + 1/2 g\eta^2``)
 # for periodic boundary conditions, see
 # - Joshua Lampert, Hendrik Ranocha (2025)
 #   Structure-preserving numerical methods for two nonlinear systems of dispersive wave equations
@@ -482,7 +482,7 @@ end
 
 # Discretization that conserves
 # - the total water (integral of ``h``) as a linear invariant
-# - the total energy
+# - the total entropy/energy (integral of ``U = 1/2 hv^2 + 1/2 g\eta^2``)
 # for reflecting boundary conditions, see
 # - Joshua Lampert, Hendrik Ranocha (2025)
 #   Structure-preserving numerical methods for two nonlinear systems of dispersive wave equations

src/equations/equations.jl

@@ -142,7 +142,7 @@ end
 """
     waterheight_total(q, equations)
 
-Return the total waterheight of the primitive variables `q` for a given set of
+Return the total waterheight ``\\eta`` of the primitive variables `q` for a given set of
 `equations`, i.e., the [`waterheight`](@ref) ``h`` plus the
 [`bathymetry`](@ref) ``b``.
 
@@ -175,7 +175,7 @@ varnames(::typeof(waterheight), equations) = ("h",)
 """
     velocity(q, equations)
 
-Return the velocity of the primitive variables `q` for a given set of
+Return the velocity ``v`` of the primitive variables `q` for a given set of
 `equations`.
 
 `q` is a vector of the primitive variables at a single node, i.e., a vector
@@ -190,7 +190,7 @@ varnames(::typeof(velocity), equations) = ("v",)
 """
     momentum(q, equations)
 
-Return the momentum/discharge of the primitive variables `q` for a given set of
+Return the momentum/discharge ``hv`` of the primitive variables `q` for a given set of
 `equations`, i.e., the [`waterheight`](@ref) times the [`velocity`](@ref).
 
 `q` is a vector of the primitive variables at a single node, i.e., a vector
@@ -230,7 +230,7 @@ still_waterdepth(q, equations::AbstractEquations{1, 1}) = equations.D
 """
     bathymetry(q, equations)
 
-Return the bathymetry of the primitive variables `q` for a given set of
+Return the bathymetry ``b`` of the primitive variables `q` for a given set of
 `equations`.
 
 `q` is a vector of the primitive variables at a single node, i.e., a vector
@@ -268,12 +268,12 @@ end
 """
     energy_total(q, equations)
 
-Return the total energy of the primitive variables `q` for a given set of
+Return the total energy ``e`` of the primitive variables `q` for a given set of
 `equations`. For all [`AbstractShallowWaterEquations`](@ref), the total
 energy is given by the sum of the kinetic and potential energy of the
 shallow water subsystem, i.e.,
 ```math
-\\frac{1}{2} h v^2 + \\frac{1}{2} g \\eta^2
+e(\\eta, v) = \\frac{1}{2} h v^2 + \\frac{1}{2} g \\eta^2
 ```
 in 1D, where ``h`` is the [`waterheight`](@ref),
 ``\\eta = h + b`` the [`waterheight_total`](@ref),
@@ -294,7 +294,7 @@ varnames(::typeof(energy_total), equations) = ("e_total",)
 """
     entropy(q, equations)
 
-Return the entropy of the primitive variables `q` for a given set of
+Return the entropy ``U`` of the primitive variables `q` for a given set of
 `equations`. For all [`AbstractShallowWaterEquations`](@ref), the `entropy`
 is just the [`energy_total`](@ref).
 
@@ -311,7 +311,7 @@ varnames(::typeof(entropy), equations) = ("U",)
 """
     energy_total_modified(q_global, equations, cache)
 
-Return the modified total energy of the primitive variables `q_global` for the
+Return the modified total energy ``\\hat e`` of the primitive variables `q_global` for the
 `equations`. This modified total energy is a conserved quantity and can
 contain additional terms compared to the usual [`energy_total`](@ref).
 For example, for the [`SvaerdKalischEquations1D`](@ref) and the
@@ -331,25 +331,25 @@ Internally, this function allocates a vector for the output and
 calls [`DispersiveShallowWater.energy_total_modified!`](@ref).
 """
 function energy_total_modified(q_global, equations::AbstractEquations, cache)
-    e = similar(q_global.x[begin])
-    return energy_total_modified!(e, q_global, equations, cache)
+    e_mod = similar(q_global.x[begin])
+    return energy_total_modified!(e_mod, q_global, equations, cache)
 end
 
 """
-    energy_total_modified!(e, q_global, equations, cache)
+    energy_total_modified!(e_mod, q_global, equations, cache)
 
 In-place version of [`energy_total_modified`](@ref).
 """
-function energy_total_modified!(e, q_global, equations::AbstractEquations,
+function energy_total_modified!(e_mod, q_global, equations::AbstractEquations,
                                 cache)
     # `q_global` is an `ArrayPartition` of the primitive variables at all nodes
     @assert nvariables(equations) == length(q_global.x)
 
     for i in eachindex(q_global.x[begin])
-        e[i] = energy_total(get_node_vars(q_global, equations, i), equations)
+        e_mod[i] = energy_total(get_node_vars(q_global, equations, i), equations)
     end
 
-    return e
+    return e_mod
 end
 
 varnames(::typeof(energy_total_modified), equations) = ("e_modified",)
@@ -360,27 +360,27 @@ varnames(::typeof(energy_total_modified), equations) = ("e_modified",)
 Alias for [`energy_total_modified`](@ref).
 """
 @inline function entropy_modified(q_global, equations::AbstractEquations, cache)
-    e = similar(q_global.x[begin])
-    return entropy_modified!(e, q_global, equations, cache)
+    U_mod = similar(q_global.x[begin])
+    return entropy_modified!(U_mod, q_global, equations, cache)
 end
 
 """
-    entropy_modified!(e, q_global, equations, cache)
+    entropy_modified!(U_mod, q_global, equations, cache)
 
 In-place version of [`entropy_modified`](@ref).
 """
-@inline entropy_modified!(e, q_global, equations, cache) = energy_total_modified!(e,
-                                                                                  q_global,
-                                                                                  equations,
-                                                                                  cache)
+@inline entropy_modified!(U_mod, q_global, equations, cache) = energy_total_modified!(U_mod,
+                                                                                      q_global,
+                                                                                      equations,
+                                                                                      cache)
 
 varnames(::typeof(entropy_modified), equations) = ("U_modified",)
 
 # The Hamiltonian takes the whole `q_global` for every point in space
 """
     hamiltonian(q_global, equations, cache)
 
-Return the Hamiltonian of the primitive variables `q_global` for the
+Return the Hamiltonian ``H`` of the primitive variables `q_global` for the
 `equations`. The Hamiltonian is a conserved quantity and may contain
 derivatives of the solution.
 

src/equations/hyperbolic_serre_green_naghdi_1d.jl

@@ -74,7 +74,8 @@ References for the hyperbolized Serre-Green-Naghdi system can be found in
 
 The semidiscretization implemented here conserves
 - the total water mass (integral of ``h``) as a linear invariant
-- the total modified energy
+- the total modified entropy/energy (integral of ``\hat U``/``\hat e``), which is called here
+  [`entropy_modified`](@ref) and [`energy_total_modified`](@ref)
 
 for periodic boundary conditions (see Ranocha and Ricchiuto (2025)).
 Additionally, it is well-balanced for the lake-at-rest stationary solution, see
@@ -357,7 +358,7 @@ end
 
 # Discretization that conserves
 # - the total water mass (integral of ``h``) as a linear invariant
-# - the total modified energy
+# - the total modified entropy/energy (integral of ``\hat U``/``\hat e``) as a nonlinear invariant
 # for periodic boundary conditions, see
 # - Hendrik Ranocha and Mario Ricchiuto (2025)
 #   Structure-Preserving Approximations of the Serre-Green-Naghdi
@@ -520,9 +521,9 @@ end
 
 # The entropy/energy takes the whole `q` for every point in space
 """
-    DispersiveShallowWater.energy_total_modified!(e, q_global, equations::HyperbolicSerreGreenNaghdiEquations1D, cache)
+    DispersiveShallowWater.energy_total_modified!(e_mod, q_global, equations::HyperbolicSerreGreenNaghdiEquations1D, cache)
 
-Return the modified total energy `e` of the primitive variables `q_global` for the
+Return the modified total energy ``\\hat e`` of the primitive variables `q_global` for the
 [`HyperbolicSerreGreenNaghdiEquations1D`](@ref).
 It contains additional terms compared to the usual [`energy_total`](@ref)
 modeling non-hydrostatic contributions. The `energy_total_modified`
@@ -531,15 +532,15 @@ is a conserved quantity (for periodic boundary conditions).
 For a [`bathymetry_mild_slope`](@ref) (and a [`bathymetry_flat`](@ref)),
 the total modified energy is given by
 ```math
-\\frac{1}{2} g \\eta^2 + \\frac{1}{2} h v^2 +
+\\hat e(\\eta, v, w) = \\frac{1}{2} g \\eta^2 + \\frac{1}{2} h v^2 +
 \\frac{1}{6} h w^2 + \\frac{\\lambda}{6} h (1 - \\eta / h)^2.
 ```
 
 `q_global` is a vector of the primitive variables at ALL nodes.
 
 See also [`energy_total_modified`](@ref).
 """
-function energy_total_modified!(e, q_global,
+function energy_total_modified!(e_mod, q_global,
                                 equations::HyperbolicSerreGreenNaghdiEquations1D,
                                 cache)
     # unpack physical parameters and SBP operator `D1`
@@ -555,8 +556,8 @@ function energy_total_modified!(e, q_global,
     @.. h = eta - b
 
     # 1/2 g eta^2 + 1/2 h v^2 + 1/6 h^3 w^2 + λ/6 h (1 - H/h)^2
-    @.. e = 1 / 2 * g * eta^2 + 1 / 2 * h * v^2 + 1 / 6 * h * w^2 +
-            lambda / 6 * h * (1 - H / h)^2
+    @.. e_mod = 1 / 2 * g * eta^2 + 1 / 2 * h * v^2 + 1 / 6 * h * w^2 +
+                lambda / 6 * h * (1 - H / h)^2
 
-    return e
+    return e_mod
 end

src/equations/kdv_1d.jl

@@ -20,18 +20,18 @@ The KdV equation is first introduced by Joseph Valentin Boussinesq (1877) and re
 
 The semidiscretization implemented here is a modification of the one proposed by Biswas, Ketcheson, Ranocha, and Schütz (2025) for the non-dimensionalized KdV equation ``u_t + u u_x + u_{x x x} = 0.``
 
-The semidiscretization looks the following:
+The semidiscretization is given by:
 ```math
 \begin{aligned}
-  \eta_t+\sqrt{g D} D_1\eta+ 1 / 2 \sqrt{g / D} \eta D_1 \eta +  1 / 2 \sqrt{g / D} D_1 \eta^2 +1 / 6 \sqrt{g D} D^2 D_3\eta &= 0.
+  \eta_t + \sqrt{g D} D_1\eta + 1 / 2 \sqrt{g / D} \eta D_1 \eta +  1 / 2 \sqrt{g / D} D_1 \eta^2 + 1 / 6 \sqrt{g D} D^2 D_3\eta &= 0.
 \end{aligned}
 ```
 where ``D_1`` is a first-derivative operator, ``D_3`` a third-derivative operator, and ``D`` the still-water depth.
 
 It conserves
 - the total water mass (integral of ``\eta``) as a linear invariant
 and if upwind operators (``D_3 = D_{1,+} D_1 D_{1,-}``) or wide-stencil operators (``D_3 = D_1^3``) are used for the third derivative, it also conserves
-- the energy (integral of ``1/2\eta^2``)
+- the entropy/total energy (integral of ``U = 1/2\eta^2``)
 
 for periodic boundary conditions.
 
@@ -279,11 +279,11 @@ end
 """
     energy_total(q, equations::KdVEquation1D)
 
-Return the total energy of the primitive variables `q` for the
+Return the total energy ``e`` of the primitive variables `q` for the
 [`KdVEquation1D`](@ref). For the KdV equation, the total energy consists
 only of the potential energy, given by
 ```math
-\\frac{1}{2} g \\eta^2
+e(\\eta) = \\frac{1}{2} g \\eta^2
 ```
 where ``\\eta`` is the [`waterheight_total`](@ref) and ``g`` is the
 [`gravity`](@ref).
@@ -299,7 +299,7 @@ end
 """
     entropy(q, equations::KdVEquation1D)
 
-Return the entropy of the primitive variables `q` for the [`KdVEquation1D`](@ref).
+Return the entropy ``U`` of the primitive variables `q` for the [`KdVEquation1D`](@ref).
 For the KdV equation, the `entropy` is the same as the [`energy_total`](@ref).
 
 `q` is a vector of the primitive variables at a single node, i.e., a vector