Solution

ID: past-exam-of-the-probability-statistics-and-options-ii-course-of-the-university-of-oxford/2007/p/4/d/solution

The Gershgorin discs of have radii . They too are disjoint and have one eigenvalue each. The disc centered at therefore improves the final bound to
It selects the same eigenvalue as before because all other discs lie a fixed positive distance from the disc centered at .

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