--- a/grid.jl	Tue Dec 18 14:51:41 2018 +0100
+++ b/grid.jl	Tue Jan 08 11:17:20 2019 +0100
@@ -3,26 +3,31 @@
 abstract type Grid end
 
 function numberOfDimensions(grid::Grid)
-    error("Not yet implemented")
+    error("Not implemented for abstact type Grid")
 end
 
 function numberOfPoints(grid::Grid)
-    error("Not yet implemented")
+    error("Not implemented for abstact type Grid")
 end
 
 function points(grid::Grid)
-    error("Not yet implemented")
+    error("Not implemented for abstact type Grid")
 end
 
 # TODO: Should this be here?
 abstract type BoundaryId end
 
-# TODO: Move to seperate file.
-# Prefer to use UInt here, but printing UInt returns hex.
+# EquidistantGrid is a grid with equidisant grid spacing per coordinat
+# direction. The domain is defined through the two points P1 = x̄₁, P2 = x̄₂
+# by the exterior product of the vectors obtained by projecting (x̄₂-x̄₁) onto
+# the coordinate directions. E.g for a 2D grid with x̄₁=(-1,0) and x̄₂=(1,2)
+# the domain is defined as (-1,1)x(0,2).
 struct EquidistantGrid <: Grid
-    numberOfPointsPerDim::Tuple
-    limits::NTuple{2,Tuple} # Stores the points at the lower and upper corner of the domain.
-                            # e.g (-1,0) and (1,2) for a domain of size (-1,1)x(0,2)
+    numberOfPointsPerDim::Tuple # First coordinate direction stored first, then
+                                # second, then third.
+    limits::NTuple{2,Tuple} # Stores the two points which defines the range of
+                            # the e.g (-1,0) and (1,2) for a domain of size
+                            # (-1,1)x(0,2)
 
     # General constructor
     function EquidistantGrid(nPointsPerDim::Tuple, lims::NTuple{2,Tuple})
@@ -34,17 +39,25 @@
         #       i.e the domain length is positive for all dimensions
         return new(nPointsPerDim, lims)
     end
-    # 1D constructor which can be called as EquidistantGrid(m, (x_l,x_r))
-    function EquidistantGrid(nPointsPerDim::Int, lims::NTuple{2,Int})
+    # 1D constructor which can be called as EquidistantGrid(m, (xl,xr))
+    function EquidistantGrid(nPointsPerDim::Integer, lims::NTuple{2,Integer})
         return EquidistantGrid((nPointsPerDim,), ((lims[1],),(lims[2],)))
     end
 
 end
 
+# Returns the number of dimensions of an EquidistantGrid.
+#
+# @Input: grid - an EquidistantGrid
+# @Return: numberOfPoints - The number of dimensions
 function numberOfDimensions(grid::EquidistantGrid)
     return length(grid.numberOfPointsPerDim)
 end
 
+# Computes the total number of points of an EquidistantGrid.
+#
+# @Input: grid - an EquidistantGrid
+# @Return: numberOfPoints - The total number of points
 function numberOfPoints(grid::EquidistantGrid)
     numberOfPoints = grid.numberOfPointsPerDim[1];
     for i = 2:length(grid.numberOfPointsPerDim);
@@ -53,24 +66,41 @@
     return numberOfPoints
 end
 
-# TODO: Decide if spacings should be positive or if it is allowed to be negative
-#       If defined as positive, then need to do something extra when calculating the
-#       points. The current implementation works for arbitarily given limits of the grid.
+# Computes the grid spacing of an EquidistantGrid, i.e the unsigned distance
+# between two points for each coordinate direction.
+#
+# @Input: grid - an EquidistantGrid
+# @Return: h̄ - Grid spacing for each coordinate direction stored in a tuple.
 function spacings(grid::EquidistantGrid)
-    h = Vector{Real}(undef, numberOfDimensions(grid))
-    for i ∈ eachindex(h)
-        h[i] = (grid.limits[2][i]-grid.limits[1][i])/(grid.numberOfPointsPerDim[i]-1)
+    h̄ = Vector{Real}(undef, numberOfDimensions(grid))
+    for i ∈ eachindex(h̄)
+        h̄[i] = abs(grid.limits[2][i]-grid.limits[1][i])/(grid.numberOfPointsPerDim[i]-1)
     end
-    return Tuple(h)
+    return Tuple(h̄)
 end
 
+# Computes the points of an EquidistantGrid as a vector of tuples. The vector is ordered
+# such that points in the first coordinate direction varies first, then the second
+# and lastely the third (if applicable)
+#
+# @Input: grid - an EquidistantGrid
+# @Return: points - the points of the grid.
 function points(grid::EquidistantGrid)
+    # Compute signed grid spacings
+    dx̄ = Vector{Real}(undef, numberOfDimensions(grid))
+    for i ∈ eachindex(dx̄)
+        dx̄[i] = (grid.limits[2][i]-grid.limits[1][i])/(grid.numberOfPointsPerDim[i]-1)
+    end
+    dx̄ = Tuple(dx̄)
+
     nPoints = numberOfPoints(grid)
     points = Vector{NTuple{numberOfDimensions(grid),Real}}(undef, nPoints)
+    # Compute the points based on their Cartesian indices and the signed
+    # grid spacings
     cartesianIndices = CartesianIndices(grid.numberOfPointsPerDim)
     for i ∈ 1:nPoints
         ci = Tuple(cartesianIndices[i]) .-1
-        points[i] = grid.limits[1] .+ spacings(grid).*ci
+        points[i] = grid.limits[1] .+ dx̄.*ci
     end
     return points
 end