Function sub_surface 

pub fn sub_surface<T>(
    backend: ComputeBackend,
    a: &SurfaceField<T>,
    b: &SurfaceField<T>,
) -> SurfaceField<T>
where
    T: Copy + Send + Sync + Sub<Output = T>,

Difference of two surface fields — internal faces and every boundary patch.

Name, mesh, and boundary conditions come from a. Units: both operands are the same physical quantity.

Panics

Panics if the internal fields or any patch pair differ in length.