Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2024/ii/paper-1/41a/b/iii/solution

If , the splitting commutator vanishes, but the backward-Euler resolvents still contribute
Thus commutativity alone does not change the order: the local error remains and the global method remains first order, barring an additional special cancellation.

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