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Andreas Marek authored
With the configure option "--enable-single-precision" ELPA1 is build with single-precision (half-words) only. The best precision in single-precision (float or complex) is 2^-23 ~ 1.2e-7. The accuracy of the error residual of ELPA1 in single-precision mode is of the order 1e-4 to 1e-5. The orthogonality of the EV's is fullfilled up to about ~1e-6. Thus the precision of ELPA1 in single-precision mode is roughly 100 - 1000 times less than the best achievable precison. This is consistent with the double-precision mode, where also a factor of 100 - 1000 less precision than the theoretical best one is found. The float EVs are identical to the double EVs to at least 1e-2, the precision of the EVs is thus about 1e-7/1e-2 = 1e5 times lower than the best theoretical precision. If the same holds for the double precision calculations, this implies that the double precision results can also be only trusted on the level 1e-11 (5 orders of magnitude larger than the best theoretical precision) The best speed-up compared to the double precision calculation is a factor of two. This is by far not achieved yet, since the singl precision version is not at all optimized at the moment
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