R help - Aug 2011 - Lm gives different results depending on x-bit architecture

Dear all,

I have encountered problem when developing application. My linear regression
does give different results depending on architecture.

Following example describes my problem perfectly.

    xxx <- data.frame(a=c(0.2,0.2,0.2,0.2,0.2),b=c(7,8,9,10,11))
    lm(a~b,xxx)
    summary(lm(a~b,xxx))$r.squared

returns on 32-bit R:

    Call:
    lm(formula = a ~ b, data = xxx)
?
    Coefficients:
    (Intercept)??????????? b?
    ??2.000e-01?? -1.503e-18?
?
    >summary(lm(a~b,xxx))$r.squared
    [1] 0

and on 64-bit R:

    Call:
    lm(formula = a ~ b, data = xxx)
?
    Coefficients:
    (Intercept)??????????? b?
    ?  2.0e-01??           0
?
    >summary(lm(a~b,xxx))$r.squared
    [1] NA

It is very easy to notice slope should be 0 in the above case. I also
understand it is related to the precision of 32 and 64 bit and dependant on
how those are internally written, but maybe someone had this problem and
found any solution.

With regards,
Adam.



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On 29.08.2011 13:54, AdamMarczak wrote:
> Dear all,
>
> I have encountered problem when developing application. My linear
regression
> does give different results depending on architecture.
>
> Following example describes my problem perfectly.
>
>      xxx<- data.frame(a=c(0.2,0.2,0.2,0.2,0.2),b=c(7,8,9,10,11))
>      lm(a~b,xxx)
>      summary(lm(a~b,xxx))$r.squared
>
> returns on 32-bit R:
>
>      Call:
>      lm(formula = a ~ b, data = xxx)
>
>      Coefficients:
>      (Intercept)            b
>        2.000e-01   -1.503e-18
>
>      >summary(lm(a~b,xxx))$r.squared
>      [1] 0
>
> and on 64-bit R:
>
>      Call:
>      lm(formula = a ~ b, data = xxx)
>
>      Coefficients:
>      (Intercept)            b
>         2.0e-01             0
>
>      >summary(lm(a~b,xxx))$r.squared
>      [1] NA
>
> It is very easy to notice slope should be 0 in the above case. I also
> understand it is related to the precision of 32 and 64 bit
Not necessarily, since the same precision is used by R. It may even be 
the result of using different compilers (or just compiler versions) for 
producing the 32-bit and the 64-bit version.
> and dependant on
> how those are internally written, but maybe someone had this problem and
> found any solution.
If you want to see if b is numerically equal to zero, use all.equal().

Uwe Ligges

>
> With regards,
> Adam.
>
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Lm-gives-different-results-depending-on-x-bit-architecture-tp3776027p3776027.html
> Sent from the R help mailing list archive at Nabble.com.
>
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