Origami & Folding
what one sheet can do
Series

Symmetry — the series

5 essays on one idea, from the one that introduces it to the one that assumes the rest.
  1. 2345678910-0.15-0.1-0.0500.050.10.15discsshortfall of the symmetric search14.6%1.7%0.0%-0.0%5.6%0.5%10.8%10.4%4.7%symmetry: mirror · both searches at 90 restartsneither number is a proved optimum — this compares two searches

    When symmetry costs

    Design software and designers both reach for symmetry, and for a good reason: it makes the search enormously easier. It is a heuristic and not a theorem, and how much it gives away can be measured — including the case where the optimum is symmetric about an axis nobody imposed.

    part 1 · design
  2. 23456789101105101520flapshow much the requirement costs, per cent14.61.70.0-0.05.60.510.810.44.72.8

    The shapes the optimum has

    Requiring a circle packing to be its own mirror image halves the number of coordinates a search has to find, so the same effort covers a much smaller space. Whether that helps depends on something the search cannot know in advance — whether the best packing was symmetric — and measured flap count by flap count the answer alternates without a pattern anybody could use.

    part 2 · design
  3. The preliminary base: 8 symmetries, 112 letteringsthe bar is the share of letterings the symmetry carries to themselvesa quarter turnnone of 112 — this symmetry cannot be foldeda half turnnone of 112 — this symmetry cannot be foldedthree quarters of a turnnone of 112 — this symmetry cannot be foldeda mirror across the sheet12 of 112a mirror up the sheet12 of 112a mirror in one diagonal12 of 112a mirror in the other diagonal12 of 112

    The symmetry the letters cannot keep

    Every pattern in this subject is drawn symmetric and the symmetry is always quoted of the drawing. A folded object is a drawing and a lettering together, so a symmetry survives only if the letters keep it — and the preliminary base loses every rotation while the square twist, drawn with the same eight, loses the other half.

    part 3 · design
  4. the impossible lettering, on ordinary patchessquare ×140 creases16 vertices · every condition holds · no forced loopsquare ×2144 creases64 vertices · every condition holds · no forced loopsquare ×3312 creases144 vertices · every condition holds · no forced looptriangular ×1116 creases48 vertices · every condition holds · no forced looptriangular ×2424 creases192 vertices · every condition holds · no forced loophexagonal ×1116 creases48 vertices · every condition holds · no forced loophexagonal ×2424 creases192 vertices · every condition holds · no forced loophexagonal ×3924 creases432 vertices · every condition holds · no forced loopthe bar is the crease count; the note is what the ordinary checks said

    The symmetry a gluing adds

    A patch of a tessellation has whatever symmetry its outline allows — a few reflections, a rotation or two. Glue its edges and it acquires translations, and a lettering of the glued sheet has to be invariant under them. That is a much stronger requirement than a lettering of the patch, and it is why one answer covers every patch at once.

    part 4 · design
  5. how far each search is from the best packing knownboth at 120 restarts of 6,000 steps; nothing below zero is possible02461011121314151617181920discsshort of the best packing known, per centthe free searchbest: a mirrorbest: a half-turnbest: a quarter-turn

    Equal effort was counted in steps

    A circle-packing search required to be symmetric was found to beat a free search of the same effort, and the reason given was that a smaller space is easier to search. Past eleven discs the test gets sharp: the free search falls behind the best packings known, 0.13 per cent at ten discs and 6.07 at twenty, and a symmetric search leads it by as much as 4.18. But tighten the free search's packings to the arrangement they were heading for and most of that shortfall disappears — at twenty discs, all of it. Give the free search twice the steps and the lead reverses. The effort was equal in steps and unequal in what a step does: a symmetric search moves half as many coordinates, so each is moved twice as often.

    part 5 · design

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