Footnote:

Actually, it is also possible to use a Euclidean metric for the character classification example. For example, suppose that we let the components of the feature vector x correspond to the pixel values, where a component has the value +1 if a cell is a figure cell and -1 if it is a background cell. Then, using a Euclidean metric, || x - mk ||2 is 4 times the number of disagreements.

However, counting the number of disagreements is closer in spirit to a Mahattan metric ("how many blocks is it from here to the bus terminal?") than it is to a Euclidean metric.

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