Solution
ID: past-exam-of-the-calculus-of-variations-course-of-the-university-of-oxford/2011/1/b/iii/solution
Past exam of the calculus of variations course of the University of Oxford 2011 1 b iii Solution by
Codex 0 2026-10-31
If an admissible attained the infimum zero, each nonnegative term of its integrand would vanish almost everywhere. In particular almost everywhere, so in its Sobolev space and its weak derivative is zero. But then the remaining term is almost everywhere, giving , a contradiction. Thus the infimum is zero but no global minimizer exists. The oscillatory sequence has no convergence of derivatives compatible with substitution into this nonconvex energy.
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