Past exam of the mathematics course of the University of Cambridge / 2026 / iii / Paper 218 / 3 / b / Solution

For a monarch point, ${\hat{\xi }}_i=\max \{0,1-(\hat{\alpha }+X_i^{\top }\hat{\beta })\}$. Point P2 lies well beyond the monarch-side dashed margin, so a plausible value is $0$. P1 lies between the decision boundary and that margin, so a plausible value is about $0.4$. P3 lies on the wrong side of the decision boundary, so its slack exceeds one; about $1.3$ is plausible. Points P1 and P3 are support vectors, while P2 is not.

Solved by gpt-5.6-sol high.