Single Precision by Default? ... lots of auxiliary variables to cast

Question

MikeStein 2011-6-3

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/8727-single-precision-by-default-lots-of-auxiliary-variables-to-cast

编辑： Scott Gordon 2023-1-22

Hi all,

I have an algorithm that I'd like to run using single precision instead of the default double precision. However, this algorithm uses many many auxiliary variables to store physical parameters that I'm simulating, and I really don't want to cast each and every one of them... Is there a way to set single precision to be the default? Otherwise, do you all have any suggestions?

Another complication that may matter... I set up the simulation parameters in an outside script, before calling a function with my primary algorithm. Both the outside script and the algorithm function contain a number of theses auxiliary variables (changing spatial grids, electromagnetic fields, and other physical parameters)

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2011-6-3

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/8727-single-precision-by-default-lots-of-auxiliary-variables-to-cast#answer_12030

There is no way to set single precision by default.

3 个评论
显示 1更早的评论隐藏 1更早的评论

Walter Roberson 2018-9-11

Unfortunately it would be difficult to figure out what these links refer to now that the newsreader is gone :(

There is feature() and system_dependent() calls that can set the default precision. No seems to know what happens if you call library routines after having set these.

In a discussion about setting the round-off mode using feature() I read a credible claim that MATLAB reset the mode after every external call. It is plausible that MATLAB might reset precision after every external call as well.

Stephen23 2018-9-11

https://web.archive.org/web/20150829000041/http://www.mathworks.com/matlabcentral/newsreader/view_thread/170061

https://web.archive.org/web/20161117050130/http://www.mathworks.com/matlabcentral/newsreader/view_thread/155369

请先登录，再进行评论。

Answer 2

Sean de Wolski 2011-6-3

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/8727-single-precision-by-default-lots-of-auxiliary-variables-to-cast#answer_12024

在 MATLAB Online 中打开

How does it hurt if the other variables are double precision, the lowest precision will be kept.

single(magic(3)).*magic(3);
class(ans)
ans =
   single

2 个评论
显示无隐藏无

MikeStein 2011-6-3

Thanks both of you for your replies! I did find a way to 'trickle' down the single precision by casting a limited set of initial variables. I wish there was a Matlab feature for this though...

-Mike

Scott Gordon 2023-1-22

编辑：Scott Gordon 2023-1-22

The example given is clearly cheating, .* is a kind of cast.

The two things not mentioned - a) Matlab is a HUGE memory hog and manages memory very inefficiently.

b) any number can be cast to anything (within reason), but that does not manage memory at all.

The slow answer is: do the calculations in double, cast to single and throw out the double.

In some cases you can cast to single first, and do the calculation after. However largely this just rains down errors, because Marlab's default is double. One is tempted to roll over in so many ways, but memory management is not one of them. Since Matlab manages memory poorly, one is forced to manage memory MANUALLY - which is a major pain.

请先登录，再进行评论。