Update the Neighborhood

The neighborhood around a winning node (shown shaded). 

The neighborhood is usually deemed to include the winning node. 

The size of the neighborhood around the winning node decreases as training progresses. 

In equation (3.4), f(d) is a function that describes how the size of the adjustment to the weights depends on the distance that a particular node in the neighborhood is from the winning node. This function might be the reciprocal of the distance between the winning node and a neighborhood node, measured across the lattice, or any other appropriate function that ensures that nearby nodes are treated differently from those that are far away. We shall consider several possible forms for this function in section 3.7.3. 

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