[R] RMySQL for Windows

[Duncan Murdoch]

On 20 Nov 2003 08:50:00 -0500, "Arend P. van der Veen"
<apv at capital.net> wrote :

>Hi all,
>
>I have been reviewing previous messages about installing RMySQL under
>windows.  My configuration is WinXP, MySQL 4.0.14-max-debug and R
>1.8.0.  I have been able install RMySQL.  However, I do have a question:
>
>When I type
>
>>library(RMySQL)
>
>I get the following:
>
>    Warning message: 
>    DLL attempted to change FPU control word from 8001f to 9001f 
>
>Based on previous messages I have concluded that this should not cause
>me problems.
>
>Is this correct ?

It's hard to answer that.  These are the issues:

A DLL loaded by the RMySQL package has altered the floating point
precision, to reduce it from 64 bit precision to 53 bits.  R saw that,
and responded by changing it back.  

If the DLL leaves it alone in the future, this won't cause any
problems for R.  This is likely the case, but it's not guaranteed:
some libraries will change it again.  R won't check again, so this
means that future calculations in R will not be carried out in the
environment under which they were designed and tested, and are likely
to be less accurate.

It could conceivably cause problems for the DLL, but this seems pretty
unlikely.  If some routine in the DLL relied on a certain amount of
rounding error, it might not function under the increased precision.
I doubt if RMySQL does a lot of floating point computation, so this
isn't something I'd worry about.

So I'd conclude that this probably won't cause you problems, but it
might.

Duncan Murdoch