Solving Sudoku puzzles is one of the most popular pastimes in the world.
Puzzles range in difficulty from easy to very challenging; the hardest puzzles
tend to have the most empty cells. The current paper explains and compares
three algorithms for solving Sudoku puzzles. Backtracking, simulated annealing,
and alternating projections are generic methods for attacking combinatorial
optimization problems. Our results favor backtracking. It infallibly solves a
Sudoku puzzle or deduces that a unique solution does not exist.
We investigate a robust penalized logistic regression algorithm based on a
minimum distance criterion. Influential outliers are often associated with the
explosion of parameter vector estimates, but in the context of standard
logistic regression, the bias due to outliers always causes the parameter
vector to implode, that is shrink towards the zero vector. Thus, using
LASSO-like penalties to perform variable selection in the presence of outliers
can result in missed detections of relevant covariates.
Tensors are multi-way arrays, and the Candecomp/Parafac (CP) tensor
factorization has found application in many different domains. The CP model is
typically fit using a least squares objective function, which is a maximum
likelihood estimate under the assumption of i.i.d. Gaussian noise. We
demonstrate that this loss function can actually be highly sensitive to
non-Gaussian noise. Therefore, we propose a loss function based on the 1-norm
because it can accommodate both Gaussian and grossly non-Gaussian
perturbations.