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Constructing a Linear Classifier from Known Decision-Boundary Points
Construct a hyperplane from known decision-boundary points, use signed distances for classification, and extend the method to noisy boundary estimates with orthogonal least squares.
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Binary Circles, Hamiltonian Cycles and de Bruijn Sequences
A small combinatorial puzzle about circular binary words whose windows are all distinct turns out to be a question about Hamiltonian cycles in de Bruijn graphs. I count the arrangements, sum their numeric encodings up to a word length of 64 bits, and end with the multiplication trick that uses such a word to locate a set bit.
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Almost-Equal Isosceles Triangles: When Height Nearly Matches Base
An exploration of a curious class of integer-sided isosceles triangles whose height differs from the base by exactly one. What begins as a simple geometric question quickly leads to Pell equations and elegant recurrences.
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Online Estimation: Updating the Inverse Covariance Matrix
Deriving Woodbury and Sherman-Morrison updates for the scatter matrix step by step, handling the singular startup phase explicitly, and verifying the reported covariance and precision with Python and R.
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Building Intelligent Agents for Connect-4: Final Considerations
The remaining techniques, an honest accounting of what each optimization was actually worth, the ideas which did not work, and why a perfect-playing Connect-4 agent has learned nothing at all.