[R] drawing a circle using symbols

[Prof Brian Ripley]

?symbols says

   inches: If 'inches' is 'FALSE', the units are taken to be those of
           the x axis.

Note, 'the x axis' and you have not ensured the x and y axes have the same 
scale.  Try

plot(c(-10,10), c(-10,10), asp=1, type="n")
symbols(x=1,y=-1,circles=5,inches=FALSE, add=TRUE
curve(3*x+1,-10,10,1000,add=TRUE)
abline(v=c(-2,1))
abline(h=c(-1,-5,4))

which works for me.  (eqscplot in MASS is another way to do this.)

On Tue, 29 Nov 2005, Troels Ring wrote:

> Dear friends, I was drawing a circle with centrum in (1,-1) and
> radius 5 to show my girl that the line y=3*x+1 goes through (1,4) and
> (-2,-5) of the circle, but on Windows XP, R 2.20 the drawing was not
> good at all, and the known solutions were not shown in the graph. I
> guess I got it wrong? Is this use not intended ?
>
> Best wishes
> Troels Ring, MD
> Aalborg, Denmark
>
> symbols(x=1,y=-1,circles=5,inches=FALSE, xlim=c(-10,10),ylim=c(-10,10))
> curve(3*x+1,-10,10,1000,add=T)
> abline(v=c(-2,1))
> abline(h=c(-1,-5,4))
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595