Document BoundaryFunction (#83)

Co-authored-by: Ivan Utkin <iutkin@ethz.ch>

Author: luraess

src/BoundaryConditions/boundary_function.jl

@@ -1,6 +1,6 @@
 """
     abstract type BoundaryFunction{F}
-    
+
 Abstract type for boundary condition functions with function type `F`.
 """
 abstract type BoundaryFunction{F} end
@@ -43,9 +43,32 @@ end
     bc.value(grid, loc, dim, I...)
 end
 
-# Create a continuous or discrete boundary function
-# if discrete = true, the function has signature f(grid, loc, dim, inds...)
-# if reduce_dims = false, the boundary condition function accepts the same number of coordinates as the number of indices
+"""
+    BoundaryFunction(fun; discrete=false, parameters=nothing, reduce_dims=true)
+
+Creates a "boundary function" object that can be use to define boundary conditions on fields.
+
+## Arguments
+- `fun`: The function defining the boundary condition.
+- `discrete=false`: If `true`, the boundary function is discrete and has the signature `f(grid, loc, dim, inds...)`.
+- `parameters=nothing`: Optional parameters to be passed to the boundary function.
+- `reduce_dims=true`: If `true`, the boundary function reduces the number of dimensions it operates on. If `false`, the function accepts the same number of coordinates as the number of indices.
+
+## Usage
+The example below shows how to use the boundary function to initialise a parabolic profile at the boundary of a 2D grid.
+
+```julia
+using Chmy
+
+arch = Arch(CPU())
+grid = UniformGrid(arch; origin=(0, 0), extent=(2, 2), dims=(10, 10))
+
+f = Field(arch, grid, Center())
+xbc = BoundaryFunction((x, ly) -> x * (ly - x); parameters=(2.0, ))
+
+bc!(arch, grid, f => (x = Dirichlet(xbc), y = Neumann()))
+```
+"""
 function BoundaryFunction(fun::Function; discrete=false, parameters=nothing, reduce_dims=true)
     RF = reduce_dims ? ReducedDimensions : FullDimensions
     discrete ? DiscreteBoundaryFunction{RF}(fun, parameters) : ContinuousBoundaryFunction{RF}(fun, parameters)

src/Fields/function_field.jl

@@ -29,7 +29,7 @@ Create a `FunctionField` on the given `grid` using the specified function `func`
 - `func::F`: The function used to generate the field values.
 - `grid::StructuredGrid{N}`: The structured grid defining the computational domain.
 - `loc`: The nodal location on the grid grid where the function field is defined on.
-- `discrete::Bool=false`: A flag indicating whether the field should be discrete. Defaults to `false`.
+- `discrete=false`: A flag indicating whether the field should be discrete. Defaults to `false`.
 - `parameters=nothing`: Additional parameters to be used by the function. Defaults to `nothing`.
 """
 function FunctionField(func::F, grid::StructuredGrid{N}, loc; discrete=false, parameters=nothing) where {F,N}