Function sub_vol 

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

Difference of two volume fields — internal field and every boundary patch.

Name, mesh, and boundary conditions come from a; the name is copied, never composed. Units: both operands are the same physical quantity.

Panics

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