Four-direction LP asymptotics

Let α\alpha be the middle real root of

401α31744α2+2240α768=0.401\alpha^3-1744\alpha^2+2240\alpha-768=0.

For odd n=2m+1n=2m+1, let LmfatL_m^{\mathrm{fat}} and LmthinL_m^{\mathrm{thin}} denote the relaxation optima on the fat and thin colour classes, respectively. For even n=2mn=2m, let LmevenL_m^{\mathrm{even}} denote the relaxation optimum on either colour class. Four-direction LP asymptotics. The three symmetry types have the common limiting ratio

limmLmfat2m+1=limmLmthin2m+1=limmLmeven2m=α.\lim_{m\to\infty}\frac{L_m^{\mathrm{fat}}}{2m+1} = \lim_{m\to\infty}\frac{L_m^{\mathrm{thin}}}{2m+1} = \lim_{m\to\infty}\frac{L_m^{\mathrm{even}}}{2m} = \alpha.

The conjecture is motivated by computed reduced linear programs in all three symmetry types and by an exact continuum upper-bound certificate in the odd-fat case. The computations suggest a common limiting slope, but do not establish the asymptotics for the finite LPs.

Sources & referencesView supporting material

Primary source

Thomas Prellberg, “No-three-in-line sets on the checkerboard grid”, arXiv:2605.09215 (2026).

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