R Under development (unstable) (2024-01-20 r85814 ucrt) -- "Unsuffered Consequences"
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> # simulate non-linear clusters (half-circles)
> simulHalfCircles <- function(n=200, prob=c(100,100), sd = 0.25)
+ {
+   # simul class
+   z <- sample(x=c(1,2), size=n, replace=TRUE, prob=prob)
+   tau <- runif(n, -4, 4)
+   eta <- rnorm(n, 0, sd)
+   x<- matrix(ncol=2, nrow = n)
+   for (i in 1:n)
+   {
+     if (z[i] == 1)
+     { x [i,] <- t(c(-1 + tau[i]+eta[i],  7 - tau[i]*tau[i]/2 + eta[i])); }
+     else
+     { x [i,] <- t(c( 1 + tau[i]+eta[i], -7 + tau[i]*tau[i]/2 + eta[i]));}
+   }
+   list(x=x, z=z)
+ }
> hc<-simulHalfCircles(200)
> plot(hc$x,hc$y,xlab='x',ylab='y',col=hc$z+1)
> 
> # simul bullsEye
> simulBullsEye <- function(n=320, prob = c(80,240), sd = c(0.25, 0.25), radius = c(1,5))
+ {
+   z <- sample(x = c(1,2), size=n, replace=TRUE, prob=prob)
+   x<- matrix(0, nrow =n, ncol=2)
+   # small circle
+   for (i in 1:n)
+   {
+     theta=runif(1)*2*pi
+     r= rnorm(1, mean=radius[z[i]], sd=sd[z[i]])
+     x[i,1]<-r*cos(theta)
+     x[i,2]<-r*sin(theta)
+   }
+   list(x=x, z=z)
+ }
> hc<-simulBullsEye()
> plot(hc$x,hc$y,xlab='x',ylab='y',col=hc$z+1)
> 
> 
> proc.time()
   user  system elapsed 
   0.20    0.04    0.23