Add ideal gas equation

src/schemes/fluid/weakly_compressible_sph/state_equations.jl

@@ -10,6 +10,7 @@ of water up to high pressures.
 - `reference_density`:       Reference density of the fluid.
 - `exponent`:                A value of `7` is usually used for most simulations.
 - `background_pressure=0.0`: Background pressure.
+- `clip_negative_pressure=false`: Negative pressure values are clipped to 0 which is necessary for `SummationDensity`.
 """
 struct StateEquationCole{ELTYPE, CLIP} # Boolean to clip negative pressure
     sound_speed         :: ELTYPE
@@ -51,17 +52,18 @@ function inverse_state_equation(state_equation::StateEquationCole, pressure)
 end
 
 @doc raw"""
-    StateEquationIdealGas(;sound_speed, reference_density, gamma, background_pressure=0.0,
+    StateEquationIdealGas( ;sound_speed, reference_density, gamma, background_pressure=0.0,
                            clip_negative_pressure=false)
 
 Equation of state to describe the relationship between pressure and density
 of a gas using the Ideal Gas Law.
 
 # Keywords
-- `sound_speed`            : Artificial speed of sound.
-- `reference_density`      : Reference density of the fluid.
-- `gamma`                  : Heat-capacity ratio
-- `background_pressure=0.0`: Background pressure.
+- `sound_speed`                 : Artificial speed of sound.
+- `reference_density`           : Reference density of the fluid.
+- `gamma`                       : Heat-capacity ratio
+- `background_pressure=0.0`     : Background pressure.
+- `clip_negative_pressure=false`: Negative pressure values are clipped to 0 which is necessary for `SummationDensity`.
 """
 struct StateEquationIdealGas{ELTYPE, CLIP}
     sound_speed         :: ELTYPE