Determine whether circles intersection
Description
circles.intersect
determines whether circles intersect with each other.
Usage
1  circles.intersect(coords, r)

Arguments
coords 
A matrix of coordinates containined the centroid of each circle. 
r 
A vector containing the radii of the circles. The have length equal to the number of rows of

Details
The algorithm is based on the premise that two circles intersect if, and only if, the distance between their centroids is between the sum and the difference of their radii. I have squared the respective parts of the inequality in the implemented algorithm.
Value
Returns a matrix of logical values indicating whether the circles intersect.
Author(s)
Joshua French
Examples
1 2 3 4 5 6 7 8  # first two intersect, then next two, last doesn't intersect any other
co = cbind(c(1, 2, 5, 6, 9), c(1, 2, 5, 6, 9))
r = c(1.25, 1.25, 1.25, 1.25, 1.25)
circles.intersect(co, r)
# nested circles
co = matrix(rep(0, 4), nrow = 2)
r = c(1, 1.5)
circles.intersect(co, r)
