Sur la notion de projection orthogonale dans un espace semi-Euclidien Original Research Article

This paper deals in new detail with the notion of orthogonal projection with respect to a quadratic form which is possibly degenerate on a finite dimensional vector space. Contrary to most important papers dealing with this question and written in the context of statistical linear models or using the language of matrices, our approach is based on the principles of affine geometry so that the fundamental machinery used can be more easily understood.