Background:
https://en.wikipedia.org/wiki/E8_lattice#Hamming_code
https://en.wikipedia.org/wiki/E8_(mathematics)
Question:
Does the following linear representation of 112 roots of $E_8$ follow from the known relationship between the (extended) Hamming code and the $E_8$ lattice?
Naively and intuitively, I don't think so. But naivete and intuition only work well during what C.S Peirce called the "abductive" phase of discovery, not afterwards. So please take a look and see what you think.
Edited 12/27/2017 to add: Please see also this follow-up question, which gives the linearization of the remaining 128 roots of $E_8$:
Linear representation of 112 roots of $E_8$:
Given any ordered string S of 9 letters over any alphabet A , S obviously contains only 8 ordered 2-tuples composed of adjacent letters, and therefore:
1) only 28 possible choices of UNordered pairs of such 2-tuples:
12,23
12,34 23,34
12,45 23,45 34,45
12,56 23,56 34,56 45,56
12,67 23,67 34,67 45,67 56,67
12,78 23,78 34,78 45,78 56,78 67,78
12,89 23,89 34,89 45,89 56,89 67,89 78,89
2) only 56 possible choices of ORDERED pairs of such 2-tuples, e.g. (23,12) as well as (12,23), etc.
Now suppose that we are allowed to read S "forward" or "backward". Then corrsponding to (1) and (2), we will have:
3) only 28 possible choices of UNordered pairs of 2-tuples:
98,87
98,76 87,76
98,65 87,65 76,65
98,54 87,54 76,54 65,54
98,43 87,43 76,43 65,43 54,43
98,32 87,32 76,32 65,32 54,32 43,32
98,21 87,21 76,21 65,21 54,21 43,21 32,21
4) only 56 possible choices of ORDERED pairs of such 2-tuples, e.g. (87,98) as well as (98,87), etc.
Hence, we will have 112 ordered pairs of ordered 2-tuples, each unqiuely identified by:
5) an index R indicating which way we R(ead) a 9-tuple (backward or forward)
6) an index O indicating which way we chose to O(rder) each Unordered pair of 2-tuples (in its "natural" order relative to our initial choice of read-direction, or in its "reverse" order relative to our initial choice of read-direction.)
7) an index L indicating which of the 28 pairing L(ocations) we chose
And clearly:
8) the 112 resulting (R,O,L) triples can be mapped in an obvious way onto the 112 roots of $E_8$ which have integer entries when the roots of $E_8$ are coordinatized in the usual way:
https://en.wikipedia.org/wiki/E8_(mathematics)
For example
Root L R O
(+1,+1,0,0,0,0,0,0) (12,23) forward natural
(+1,-1,0,0,0,0,0,0) (23,12) forward reverse
(-1,+1,0,0,0,0,0,0) (98,87) backward natural
(-1,-1,0,0,0,0,0,0) (87,98) backward reverse
9) the 112 (R,O,L) triples can be paired off in an obvious way as inverses of one another.
Edited 12/27 to add: Please also see this related "bounty" question:
The 240 vertices break into 128 verticies of a half-8-cube, and 112 vertices of the truncated 8-orthotope.
If you extend the packing of the 112 alone, you end up with the 8d semi-cubic, that is, the sets of 8 integers with even sum.
The Hamming-Code is simply the vertices of E8 in terms of the ordinary 8-cubic. You take some code like 0F, and this expands to (0,0,0,0,½,½,½,½). You then replicate this bit sequence for all sixteen coordinates, and you get a cube-cell with 16 vertices of the E8. The Leech-code does the same thing with the Leech-lattice in 24 dimensions.
I found out something very interesting about the Hamming-code: It can be constructed from the representation of E8 as D4D4 * 4. But because D4D4 can be constructed in six different ways, there is no dependency of the second nibble on the first, even if you suppose 0000 0000 and 1111 1111 is part of the code. Without this, there are 24 different Hamming-codes on this construction.
The 112 roots given here belong to an inscribed B8. In order to reach E8, you need to get an even-number of -1 in all positions.
They represent the eutactic star of B8. Two points are close neighbours, if they share one coordinate of the same sign and position, eg (2,2,0,0,0,0,0,0) and (2,0,0,0,0,-2,0,0) are adjacent.
My understanding of your scheme is to suppose the nine numbers sit like this:
This is a trace of the petrie polygon of B8, excluding one of the eight edges. I'm pretty sure that Coxeter has something to say on this, but i would have to look up that book. I think the PP for B8 is 14. This is then in some sort of right product with a group of 8 to give 112.
But i will have to play around with it tomorrow.