I have two polyhedral cones represented by their rays. I am looking to find their intersection, which would also be a polyhedral cone, hopefully efficiently. Does anybody know a way to do that?



  • $\begingroup$ More details would help. Are you trying to find the intersection numerically or give a simple description in some sense? What kind of an answer would be acceptable? What space are you working in? $\endgroup$ – Joonas Ilmavirta Aug 19 '14 at 19:43
  • 3
    $\begingroup$ At an REU in 2010, I was a part of a team that designed and implemented an algorithm along these lines as a part of a project to visualize piecewise flat manifolds. The relevant section of our paper begins at the bottom of page 8 at this link: math.arizona.edu/~asp/2010/… Hope something there is useful! $\endgroup$ – Justin Lanier Aug 19 '14 at 22:41

Presumably you are working in $\mathbb{R}^d$ for $d > 3$. There are specialized algorithms in $d=2,3$.

Here is one route. You have, essentially, what is known as the V-representation of your polytopal cones, V=vertex. An alternate representation is the H-representation, H=halfspace, the intersection of halfspaces. If you convert each cone's V-representation to an H-representation, then you have reduced your problem to intersecting all the halfspaces defining both cones.

One can convert between V- and H-representations via a variety of software packages. E.g., it can be accomplished in R; see this link. Perhaps a better place to start is polymake; see this web page.

The intersection of halfspaces can be accomplished by a wider variety of software, including polymake and qhull.


Another code you may wish to try is 4ti2's rays-function. It can also be called via polymake.


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