In mathematics, the conjugate gradient method is an algorithm for the numerical solution of particular systems of linear equations, namely those whose matrix is symmetric and positive definite. The conjugate gradient method is an iterative method, so it can be applied to sparse systems which are too large to be handled by direct methods such as the Cholesky decomposition. Such systems arise regularly when numerically solving partial differential equations.
xd3d is a simple scientific visualization tool designed to be easy to learn. It can plot 2d and 3d meshes, with shadowing, contour plots, vector fields, iso-contour (3d), as well as 3d surfaces z=f(x,y) defined by an algebraic expression or a cloud of points. It generates high quality vector PostScript files for scientific publications and still or animated bitmap images. It includes the graph plotter xgraphic.
The millenium seemed to spur a lot of people to compile "Top 100" or "Best 100" lists of many things, including movies (by the American Film Institute) and books (by the Modern Library). Mathematicians were not immune, and at a mathematics conference in July, 1999, Paul and Jack Abad presented their list of "The Hundred Greatest Theorems." Their ranking is based on the following criteria: "the place the theorem holds in the literature, the quality of the proof, and the unexpectedness of the result."