R Under development (unstable) (2023-12-13 r85679 ucrt) -- "Unsuffered Consequences"
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> 
> library(rcdd)
If you want correct answers, use rational arithmetic.
See the Warnings sections in help pages for
    functions that do computational geometry.
> 
> x <- seq(10, 90, 10)
> x <- x[x != 50]
> y <- as.numeric(x > 50)
> m <- cbind(1, x)
> 
> tanv <- m
> tanv[y == 1, ] <- (-tanv[y == 1, ])
> tanv
          x
[1,]  1  10
[2,]  1  20
[3,]  1  30
[4,]  1  40
[5,] -1 -60
[6,] -1 -70
[7,] -1 -80
[8,] -1 -90
> 
> makeV(points = tanv)
              x
[1,] 0 1  1  10
[2,] 0 1  1  20
[3,] 0 1  1  30
[4,] 0 1  1  40
[5,] 0 1 -1 -60
[6,] 0 1 -1 -70
[7,] 0 1 -1 -80
[8,] 0 1 -1 -90
attr(,"representation")
[1] "V"
> makeV(rays = tanv)
              x
[1,] 0 0  1  10
[2,] 0 0  1  20
[3,] 0 0  1  30
[4,] 0 0  1  40
[5,] 0 0 -1 -60
[6,] 0 0 -1 -70
[7,] 0 0 -1 -80
[8,] 0 0 -1 -90
attr(,"representation")
[1] "V"
> makeV(lines = tanv)
              x
[1,] 1 0  1  10
[2,] 1 0  1  20
[3,] 1 0  1  30
[4,] 1 0  1  40
[5,] 1 0 -1 -60
[6,] 1 0 -1 -70
[7,] 1 0 -1 -80
[8,] 1 0 -1 -90
attr(,"representation")
[1] "V"
> 
> 
> proc.time()
   user  system elapsed 
   0.09    0.07    0.17