Summit uses POWER9 processors, whose AltiVec SIMD engine accumulated bugs in Vectors. Pull request https://bitbucket.org/cactuscode/cactusutils/pull-requests/24/vectors-updates-for-altivec-and-knl/diff addresses these.

The pull request is from just before the Mayer release and has seen extensive discussion between @Erik Schnetter and myself as well as triggering creating a better test harness for Vectors (see #2380).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2381/update-vectors-altivec-support