A Non-Local Block is an image block module used in neural networks that wraps a non-local operation. We can define a non-local block as:

$\mathbb{z}\_{i} = W\_{z}\mathbb{y\_{i}} + \mathbb{x}\_{i}$

where $y\_{i}$ is the output from the non-local operation and $+ \mathbb{x}\_{i}$ is a residual connection.