Chores: add 3D to README & fix an assertion

README.md

@@ -51,9 +51,10 @@ a feature of the forthcoming Fortran 2028 standard.
 Examples
 --------
 ### Highlights
-Formal now supports two-dimensional (2D) operators that compute the gradient (`.grad.`) of a
-scalar field, the divergence (`.div.`) of vector field, and the arithmetic operators required 
-for expressing the advection/diffusion partial differential equation (PDE)
+Formal now supports 2D and 3D operators that compute the gradient (`.grad.`) of
+a scalar field, the divergence (`.div.`) of a vector field, and the arithmetic
+operators required for expressing the advection/diffusion partial differential
+equation (PDE)
 
 $$ \partial s / \partial t = \nabla \cdot (D \nabla s) - \nabla \cdot (\vec{v}s)$$
 

src/formal/scalar_3D_s.F90

@@ -243,7 +243,7 @@
       ,y => self%grid(y_dir) &
       ,z => self%grid(z_dir) &
     )
-      call_julienne_assert(num_points .equalsExpected. size(x)*size(y))
+      call_julienne_assert(num_points .equalsExpected. size(x)*size(y)*size(z))
 
       associate(num_blank_lines => size(y)-1)
         allocate(lines(size(header) +  num_points + num_blank_lines))