[R] unexpected behaviour of 'curve' function
Peter Dalgaard
p.dalgaard at biostat.ku.dk
Fri Nov 26 12:27:35 CET 2004
"Guazzetti Stefano" <Stefano.Guazzetti at ausl.re.it> writes:
> Dear all,
>
> curve(x^3*(1-x)^7, from = 0, to = 1)
>
> works as expected but, omitting the "xlim" or the "to"
> and "from" arguments and calling "curve" more than once:
>
> par(mfrow = c(2,2))
> for (i in 1:4)
> curve(x^3*(1-x)^7)
>
> gives an expected (al least to me) result.
> Note also that a "pu" object is returned by curve
>
> > pu
> [1] -0.1802445 1.1802445
>
> The behaviour is reproducible with both R 2.0.0
> and R 2.0.1
>
> I can see that a promise of evaluation of "pu"
> is made within curve but I cannot understand completely
> what happens.
I think the upshot is just that it is taking the "from" and "to" from
par("usr") from the previous plot and every time you do so, it expands
a little (about 4%). Notice that it does not happen if you do this:
par(mfrow = c(2,2), xaxs="i")
for (i in 1:4)
curve(x^3*(1-x)^7)
Having pu end up in the global environment looks like a bug in
delay() but I don't think it has any influence on this particular
effect.
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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