Mexican Hat Function

• There are various ways to move the points in the map in response to input, but the Mexican Hat Function is the standard.
• The idea is that you find the closest point; that's the centre of the hat.
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• You then find things around that target; that's the first circle, and the body of the hat.
• You then find things even further out; that's the second circle.
• Things inside the first circle you move toward the target; those in the second you move away.
• You follow the hat so that things closer to the centre move more in the first circle.
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• Note the Y is the data point, and the Xs are the SOM units.