QR decomposition test, sign issue
From IRC: https://irclogs.nim-lang.org/16-01-2021.html#15:08:07


  | FromDiscord | <juliuskiesian> @mratsim QR decomposition test fails in arraymancer test suite.
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15:08:34 | FromDiscord | <juliuskiesian> some of the tensor elements are off by sign.
15:10:52 | FromDiscord | <juliuskiesian> sent a code paste, see https://play.nim-lang.org/#ix=2Mdr

