## Problems computing convex hull

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Nidhi

### Problems computing convex hull

I am trying to compute the convex hull of the 2001 points in R^4 found in the attachment. They represent a part of the attainable region of a chemical reaction network that I am working on, goal is to compute the entire attainable region.

Polymake immediately gives me the following error when I try to do this:

Code: Select all

polymake: WARNING: rule cdd.convex_hull.canon: POINTED, RAYS, LINEALITY_SPACE : INPUT_RAYS failed: Error in dd_MatrixCanonicalize: 15 polymake: WARNING: rule cdd.convex_hull.redund: RAYS, RAY_SEPARATORS, LINEALITY_SPACE : INPUT_RAYS failed: Error in dd_Redundant: 15
I think the problem lies with cdd. Can you do me a favour and check whether the computation is feasible using another convex hull algorithm?
Attachments
input1.txt
(166.06 KiB) Downloaded 96 times

opfer
Developer
Posts: 68
Joined: 04 Feb 2013, 11:12

### Re: Problems computing convex hull

Hi!

I am not sure, but I think this is due to bad numerics. I do not get these errors when using your coordinates in a rational polytope.

I would never ever rely on numbers like 5.09802551220429e-18 in floating point arithmetic. I have not checked the whole dataset, but the numbers differ at least in 18 orders of magnitude. I would never expect any appropriate floating point calculations in such a setting.

Best regards,
Thomas

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