Rosenblatt's perceptron: the update, the cone, and the bound
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Amber line: the model's separating plane, perpendicular to w. Blue cone: where w must lie after k mistakes. Green wedge: every w that classifies every point correctly. Pink zigzag: the extremal run, riding the cone edge. Each step picks adversarially: among the mistakes available, one of the two whose update leaves w at the widest angle to w*.