Function difference 

pub fn difference<T: RudaPrimitive, O: RudaBinaryOp<T>>(
    input: &Array<T>,
    output: &mut Array<T>,
    scratch: &mut SharedMemory<T>,
    op: &O,
    neighbour: T,
    valid_items: usize,
    items_per_thread: usize,
    right: bool,
    has_neighbour: bool,
)

Adjacent transform in blocked order. With no external neighbour, preserve the boundary input. The operator receives (current, neighbouring).