floating point arithmetics computing in quadruple precision

13 次查看（过去 30 天）
Alain Barraud
Alain Barraud 2021-6-25
评论： Alain Barraud 2021-6-26
I try to use quadruple precision using the well know "double double" approach. Many operations seems correct however some results are wrong. To operate correctly it is necessary to avoid access 80bits register. Is it the case when running Matlab. Furthermore it would be very useful to use FMA operations which are available for AMD and Intel processors (FMA3). How to use these functions within Matlab.
Among strange results I cannot compute 1/6 with 31 correct digits. Perhaps because using double precision 6*(1/6)=1 exactly although 1/6 = 1.666666666666667e-01!!
Best regards
  9 个评论
显示 7更早的评论
Alain Barraud
Alain Barraud 2021-6-25
I'll look at your ref, I know xsum. It seems that the cleve code is available today. In the past it says that it was too slow to be useful.
Thanks a lot for your answers
alain

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Jan
Jan 2021-6-25
In Matlab 6.5 you could control the usage of the 80 bit registers:
% [UNTESTED in modern Matlab versions]
system_dependent('setprecision', 64) % Enable 80 bit registers
system_dependent('setprecision', 53) % Disable
At least on Intel CPUs using 64 bit registers was the default. I've experimented with this for XSum and a stable ACOS algorithm.
This might work also:
feature('SetPrecision', 64) % [UNTESTED in modern Matlab versions]
  3 个评论
显示 1更早的评论
Walter Roberson
Walter Roberson 2021-6-25
Current MATLAB still accepts setprecision for system_dependent() and feature() . Whether it matters is a different question.
If I recall correctly, setprecision had no effect on calculations that were punted over to the high-speed libraries.. and also IIRC, the precision was reset at unpredicable times (because it was a change to the FCW and MATLAB assumed it was not necessary to preserve the FCW.)

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Logical 的更多信息

标签

产品


版本

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by