harmonic functions and the chromatic polynomial
play

harmonic functions and the chromatic polynomial R. Kenyon (Brown) - PowerPoint PPT Presentation

harmonic functions and the chromatic polynomial R. Kenyon (Brown) based on joint work with A. Abrams, W. Lam The chromatic polynomial G ( n ) of a graph G is the number of proper colorings with n colors. (adjacent vertices have di ff erent


  1. harmonic functions and the chromatic polynomial R. Kenyon (Brown) based on joint work with A. Abrams, W. Lam

  2. The chromatic polynomial χ G ( n ) of a graph G is the number of proper colorings with n colors. (adjacent vertices have di ff erent colors) χ ( n ) = n ( n − 1)( n − 2) χ satisfies a contraction-deletion rule: χ G ( n ) = χ G − e ( n ) − χ G/e ( n ) but is # P -hard to compute in general.

  3. The Dirichlet problem 1 A graph G = ( V, E ) c : E → R > 0 the edge conductances 4 2 B ⊂ V boundary vertices 3 u : B → R boundary values Find f : V → R harmonic on V \ B 6 5 and f | B = u . X 0 = ∆ f ( x ) = c e ( f ( x ) − f ( y )) 0 y ∼ x f is the unique function with f | B = u minimizing the Dirichlet energy X c e ( f ( x ) − f ( y )) 2 E ( f ) = e = xy { edge energy

  4. A harmonic function induces a compatible orientation: an acyclic orientation with no internal sources or sinks, and no oriented paths from lower boundary values to higher boundary values. “current flows downhill” 3 1 2 4 6 9 5 7 8 10 12 11 We let Σ be the set of compatible orientations How many are there?

  5. <latexit sha1_base64="RxsiDGhzvqrolIz58PMXQCekNsY=">ACJHicbVBNSwMxFMz6WetX1aOXYCt4KrteVBApCOKxglWhW8rb9LUNZpMlyRbLsn/Gi3/FiwcrHrz4W0xrD1odCAwz7zF5EyWCG+v7H97c/MLi0nJhpbi6tr6xWdravjEq1QwbTAml7yIwKLjEhuVW4F2iEeJI4G10fz72bweoDVfy2g4TbMXQk7zLGVgntUun132klSyMwfYZCHqRt0PDezFUKGikTMkBPtAsnCRlGjt5osTQqgRNXm2Xyn7Vn4D+JcGUlMkU9XZpFHYUS2OUlgkwphn4iW1loC1nAvNimBpMgN1D5uOSojRtLJdk73ndKhXaXdk5ZO1J8bGcTGDOPITY6vMbPeWPzPa6a2e9zKuExSi5J9B3VTQa2i48poh2tkVgwdAa5+ytlfdDArCu26EoIZk/+SxqH1ZNqcHVYrp1N2yiQXbJHDkhAjkiNXJI6aRBGHskzeSUj78l78d689+/ROW+6s0N+wfv8ArYjpag=</latexit> <latexit sha1_base64="RxsiDGhzvqrolIz58PMXQCekNsY=">ACJHicbVBNSwMxFMz6WetX1aOXYCt4KrteVBApCOKxglWhW8rb9LUNZpMlyRbLsn/Gi3/FiwcrHrz4W0xrD1odCAwz7zF5EyWCG+v7H97c/MLi0nJhpbi6tr6xWdravjEq1QwbTAml7yIwKLjEhuVW4F2iEeJI4G10fz72bweoDVfy2g4TbMXQk7zLGVgntUun132klSyMwfYZCHqRt0PDezFUKGikTMkBPtAsnCRlGjt5osTQqgRNXm2Xyn7Vn4D+JcGUlMkU9XZpFHYUS2OUlgkwphn4iW1loC1nAvNimBpMgN1D5uOSojRtLJdk73ndKhXaXdk5ZO1J8bGcTGDOPITY6vMbPeWPzPa6a2e9zKuExSi5J9B3VTQa2i48poh2tkVgwdAa5+ytlfdDArCu26EoIZk/+SxqH1ZNqcHVYrp1N2yiQXbJHDkhAjkiNXJI6aRBGHskzeSUj78l78d689+/ROW+6s0N+wfv8ArYjpag=</latexit> <latexit sha1_base64="RxsiDGhzvqrolIz58PMXQCekNsY=">ACJHicbVBNSwMxFMz6WetX1aOXYCt4KrteVBApCOKxglWhW8rb9LUNZpMlyRbLsn/Gi3/FiwcrHrz4W0xrD1odCAwz7zF5EyWCG+v7H97c/MLi0nJhpbi6tr6xWdravjEq1QwbTAml7yIwKLjEhuVW4F2iEeJI4G10fz72bweoDVfy2g4TbMXQk7zLGVgntUun132klSyMwfYZCHqRt0PDezFUKGikTMkBPtAsnCRlGjt5osTQqgRNXm2Xyn7Vn4D+JcGUlMkU9XZpFHYUS2OUlgkwphn4iW1loC1nAvNimBpMgN1D5uOSojRtLJdk73ndKhXaXdk5ZO1J8bGcTGDOPITY6vMbPeWPzPa6a2e9zKuExSi5J9B3VTQa2i48poh2tkVgwdAa5+ytlfdDArCu26EoIZk/+SxqH1ZNqcHVYrp1N2yiQXbJHDkhAjkiNXJI6aRBGHskzeSUj78l78d689+/ROW+6s0N+wfv8ArYjpag=</latexit> <latexit sha1_base64="RxsiDGhzvqrolIz58PMXQCekNsY=">ACJHicbVBNSwMxFMz6WetX1aOXYCt4KrteVBApCOKxglWhW8rb9LUNZpMlyRbLsn/Gi3/FiwcrHrz4W0xrD1odCAwz7zF5EyWCG+v7H97c/MLi0nJhpbi6tr6xWdravjEq1QwbTAml7yIwKLjEhuVW4F2iEeJI4G10fz72bweoDVfy2g4TbMXQk7zLGVgntUun132klSyMwfYZCHqRt0PDezFUKGikTMkBPtAsnCRlGjt5osTQqgRNXm2Xyn7Vn4D+JcGUlMkU9XZpFHYUS2OUlgkwphn4iW1loC1nAvNimBpMgN1D5uOSojRtLJdk73ndKhXaXdk5ZO1J8bGcTGDOPITY6vMbPeWPzPa6a2e9zKuExSi5J9B3VTQa2i48poh2tkVgwdAa5+ytlfdDArCu26EoIZk/+SxqH1ZNqcHVYrp1N2yiQXbJHDkhAjkiNXJI6aRBGHskzeSUj78l78d689+/ROW+6s0N+wfv8ArYjpag=</latexit> <latexit sha1_base64="RxsiDGhzvqrolIz58PMXQCekNsY=">ACJHicbVBNSwMxFMz6WetX1aOXYCt4KrteVBApCOKxglWhW8rb9LUNZpMlyRbLsn/Gi3/FiwcrHrz4W0xrD1odCAwz7zF5EyWCG+v7H97c/MLi0nJhpbi6tr6xWdravjEq1QwbTAml7yIwKLjEhuVW4F2iEeJI4G10fz72bweoDVfy2g4TbMXQk7zLGVgntUun132klSyMwfYZCHqRt0PDezFUKGikTMkBPtAsnCRlGjt5osTQqgRNXm2Xyn7Vn4D+JcGUlMkU9XZpFHYUS2OUlgkwphn4iW1loC1nAvNimBpMgN1D5uOSojRtLJdk73ndKhXaXdk5ZO1J8bGcTGDOPITY6vMbPeWPzPa6a2e9zKuExSi5J9B3VTQa2i48poh2tkVgwdAa5+ytlfdDArCu26EoIZk/+SxqH1ZNqcHVYrp1N2yiQXbJHDkhAjkiNXJI6aRBGHskzeSUj78l78d689+/ROW+6s0N+wfv8ArYjpag=</latexit> <latexit sha1_base64="p/IPQuUDXA3DdKJKhaJ/EckwkG0=">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</latexit> <latexit sha1_base64="p/IPQuUDXA3DdKJKhaJ/EckwkG0=">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</latexit> <latexit sha1_base64="p/IPQuUDXA3DdKJKhaJ/EckwkG0=">ACa3icbVDJbhNBEO0ZtmCWmOXAdihR+JkzeRCuKBISIgDh4BwEsljrOqemriVnu5RLwnWaE78ITc+gQvfQI/jAySU1NLTe9Vrx5vlHQ+y34m6bXrN27e2ro9uHP3v3t4YOHh84EK2gqjDL2mKMjJTVNvfSKjhtLWHNFR/z0Xa8fnZF10ugvftXQvMYTLSsp0EdqMfxeaCN1SdrDR/IwbguBCt53hQvckW+LGv2Sc/jcfT0cAyfwS4IogKmgClr0UxycS78EboIu0a7gDFUgB+MwBtQlaANxau+ktVR2UnuyOi6hb95Sjd1kMRxlk2xdcBXkGzBimzpYDH8UpRGhjq6FQudmedb4eYvWS6GoGxTBUYPiFE9oFqHGmty8XVvoYCcyJVTGxhevXrN/2ixdm5V89jZ3+4uaz35P20WfLU3b6VugictLhZVQYE30CcPpbQkvFpFgMLK6BXEi2KmIcbxBDydfBdPdyZtJ/ml3tP92k8YWe85eslcsZ6/ZPvADtiUCfYr2U6eJE+T3+nj9Fn64qI1TZ/HrF/Kt35A5xhuxA=</latexit> <latexit sha1_base64="p/IPQuUDXA3DdKJKhaJ/EckwkG0=">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</latexit> <latexit sha1_base64="p/IPQuUDXA3DdKJKhaJ/EckwkG0=">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</latexit> Let F ⊂ R V be the set of functions with boundary values u and no internal extrema. Then ¯ [ F = F σ σ ∈ Σ where F σ = { f ∈ F | sign( d f ) = σ } . The F σ are convex polytopes. y 1 1.0 0.8 0.6 x y 0.4 0.2 x 0 0.2 0.4 0.6 0.8 1.0

  6. Fixed energy problem:

  7. Can we adjust edge conductances so that all bulbs burn with the same brightness?

Recommend


More recommend