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摘要
The accuracy analysis of complex floating-point multiplication done by Brent, Percival, and Zimmermann [Math. Comp., 76: 1469-1481, 2007] is extended to the case where a fused multiply-add (FMA) operation is available. Considering floating-point arithmetic with rounding to nearest and unit roundoff u, we show that their bound root 5 u on the normwise relative error vertical bar(z) over cap /z-1 vertical bar of a complex product z can be decreased further to 2u when using the FMA in the most naive way. Furthermore, we prove that the term 2u is asymptotically optimal not only for this naive FMA-based algorithm but also for two other algorithms, which use the FMA operation as an efficient way of implementing rounding error compensation. Thus, although highly accurate in the componentwise sense, these two compensated algorithms bring no improvement to the normwise accuracy 2u already achieved using the FMA naively. Asymptotic optimality is established for each algorithm thanks to the explicit construction of floating-point inputs for which we prove that the normwise relative error then generated satisfies vertical bar(z) over cap /z-1 vertical bar -> 2u as u -> 0. All our results hold for IEEE floating-point arithmetic, with radix beta, precision p, and rounding to nearest; it is only assumed that underflows and overflows do not occur and that beta(p-1) >= 24.
- 出版日期2017-3
- 单位INRIA
