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@pieter@mathstodon.xyz
Post #2923562
2026-04-29 00:29 UTC
The deflation operation can be abelianised (in some sense) to give a 2 x 2 complex matrix with eigenvalues \(\phi\) and \(\phi^{-1}\), where \(\phi\) is the square of the golden mean. If we project the lifted centres of tiles with more frequent handedness onto the left eigenspace of \(\phi^{-1}\) (spanned by \((1, -\xi\phi)\)) and colour the projected points according to the orientation of the tile, we get a pattern which is the superposition of the two triangles shown, translated so their centres coincide.
On the other hand, consider the projection onto the first coordinate. For a given tile centre, we can track its position as we continuously deform the projection from that eigenspace projection to the \((1,0)\) projection, and we can translate the region that the eigenspace projection of the point landed in as we do so, keeping the relative position of the projected point within the region fixed. This spreads out the regions, and we obtain the periodic pattern shown in the second image.
I've overlain this with hexagons, which are the images of the tiles with more frequent handedness under this projection. A short line indicates the orientation of the lifted tile. In the notation of the previous post, these lines extend from \((0,0)\) towards \((\xi^2,0)\) (for a tile in that particular orientation)
(3/n)
Replies (1)
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We can now change the projection again, going from the \((1,0)\) projection to the \((1, -1)\) projection, dragging the regions along as before. The result is that the triangles spread out further, but the grid points in adjacent triangles no longer lie on a common rectangular grid (at least, not one with the same distance between points). This is why my construction here https://mathstodon.xyz/@pieter/110520611405361464
required two steps.
But if we shift the control point to the position Peter chose, the grids become compatible, yet the regions (which must move along with the control points) fortunately don't overlap.
So far I've ignored the tiles with less frequent handedness. From the second image, we can deduce regions that must correspond to their control points by considering their 'H8' neighbourhoods and looking at the intersections of the regions associated to these tiles (If this isn't clear, this post on empires of turtle tilings may help explain the general principle: https://mathstodon.xyz/@pieter/111696562690124891)
(4/n)
Open ##2923563