4D Compounds from verf

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ndl
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4D Compounds from verf

Post by ndl » Tue May 14, 2019 6:49 pm

I'm having inconsistency in being able to create 4D compounds from compound verf. Sometimes it works and sometimes not even from the same verf, for example the compound of 2 icosahedra should create a compound of 10 ex, but I was only able to do that once and now it doesn't work. Also 2 dodecahedra verf should create a valid 4D compound as well as facetings thereof, but I have not gotten any of those to work at all. Thanks for your help.

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robertw
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Re: 4D Compounds from verf

Post by robertw » Wed May 15, 2019 1:24 am

I was happy to get vertex figures to work for all 1849 uniform polychora and a bunch of scaliforms, and even some compounds.

But yes, compounds are tricky because there's often multiple ways to match at each vertex, and if you take the wrong branch it can continue infinitely far without ever connecting up again.

Maybe some day I'll try to improve it, but it would probably be better to deal with compounds in another way. The ones where components don't share vertices could never be done with vertex figures anyway.

ndl
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Re: 4D Compounds from verf

Post by ndl » Sun May 19, 2019 2:35 am

If I take the compound of 10gax included with Stella4D, choose the vertex figure, press convert to base model, then try to create Uniform 4D it doesn't work. So what is the way you created the original file that allows it to work?

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Re: 4D Compounds from verf

Post by robertw » Sun May 19, 2019 5:04 am

Hmm, I don't remember, but could just come down to what order the faces are defined in, which causes it to grow each vertex in a different order.

ndl
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Re: 4D Compounds from verf

Post by ndl » Tue Jun 04, 2019 4:55 am

I was able to make more compounds from verfs if I facetted that 10gax one that was built in and modifying the 5oct compound:
Compound verfs.zip
(6.23 KiB) Downloaded 38 times
But I couldn't get any others to work.

ndl
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Re: 4D Compounds from verf

Post by ndl » Wed Jun 05, 2019 12:47 am

Another thing that makes compounds confusing in stella 4D is that in the info it counts each cell and vertex separately even the ones that are corealmic/coincident.
Also I couldn't rename the duals of 4Ds created from verf without resaving them as straight 4Ds.
Thanks for all your help.

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robertw
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Re: 4D Compounds from verf

Post by robertw » Thu Jun 06, 2019 1:49 pm

I think that's correct, to count compound vertices twice, and corealmic cells twice. They are two separate items that happen to be in the same place/plane. Same happens in 3D, coplanar faces are still two faces.

Re 4D dual naming, you mean you'd like to be able to name the dual even when only saving the model as a 3D vertex figure? Not sure where that could go.

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Re: 4D Compounds from verf

Post by ndl » Fri Jun 07, 2019 5:31 am

Yes they are still two faces in the total count, but Stella is able to differentiate types for viewing. In 4D that is not the case, it considers them all the same type of cell and you can't display the different instances. Also in the cell viewing option it will say "x cells of this type" referring but since it's displaying all of the corealmic ones at the same time that's not really true.

On the built-in library the regulars have their duals named appropriately despite being verfs.

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Re: 4D Compounds from verf

Post by robertw » Sun Jun 09, 2019 2:26 am

Ah, been a while since I did this so I'd forgotten some of how it worked, but turns out I did already add a way to set the dual name in the vertex figure.

Just add "cell-of-" at the start of the dual name. The dual of the vertex figure is a cell of the dual. This tells Stella to extract the name of the final dual.

Stella doesn't have as full an understanding of symmetry and cell types in 4D. I use various heuristics, and it mostly works to determine which cells are of different types , but compounds don't work so well because it's really several separate polytopes. The heuristics work on the topology so it can't tell how one polytope relates to the whole.

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Re: 4D Compounds from verf

Post by ndl » Tue Jun 11, 2019 3:29 am

Ok got it thanks

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