# [R] Drawing a circle

Chuck Cleland ccleland at optonline.net
Thu May 19 13:26:02 CEST 2005

```See ?symbols.  For example:

> a <- 1.975 # valore x del centro
> b <- 1.215 # valores y del centro
> r <- 1.460 # radio
> plot(0,0, type = "n", ylim=c(b - r, b + r), xlim=c(a - r, a + r))
> symbols(x = a, y = b, circles = r)

Mario Morales wrote:
> Hi.
>
> I need to draw a circle whit center (a,b) and radio r. So I use the
> R code below
>
> a<-1.975 # valore x del centro
> b<-1.215 # valores y del centro
> x1<-seq(a-r,a+r,by=0.01); #los valores de x
> yp<-sqrt(r^2-(x1-a)^2)+b; # los valores y a partir de la raíz positiva
> yn<-(-1)*sqrt(r^2-(x1-a)^2)+b; # los valores y a partir de la raíz negativa
> x<-c(x1,x1);  y<-c(yp,yn);
>
> plot(x,y,type="l",ylab="",xlab="",xlim=range(x),ylim=range(y));
>
>
> My circle have two problems.
>
> First. I don't want the horizontal line and I don't know how avoid
> it.
>
> Second. It is shaped like ellipse. I need adjust the x and y scales,
> but I don't know how.
>
> Can you help me???
>
> there is another way to draw a circle whit R ?
>
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>
>

--
Chuck Cleland, Ph.D.
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