% This example illustrates the fact that the standard backward
% rounding-error bound for the Cholesky decomposition can be much larger
% than the backward error itself.  It generates a symmetric positive
% definite matrix of order n with norm 1 and condition number 10^t.  It
% then computes the Cholesky factor R in single precision and the
% backward error A - R'*R in double precision.  The classical bound is
% printed out for comparison (see Higham, Accuracy and Stability of
% Numerical Algorithms, 2nd edition, p. 198).

% This script can be used to explain how a divergent sum can converge in
% finite precision arithmetic--in this case in 2-digit decimal
% floating-point arithmetic.  In the first run, the sum becomes
% stationary when it reaches a value of 3.9.  The second run prints out
% enough additional information to show what is going on.  The teacher
% can supply running comments.

% This example solves a quadratic equation using the standard quadratic
% formula.  The smallest root is completely inaccurate.  A cure is
% illustrated.   The script produces comments as it proceeds.

% This script generates a a matrix A of order 100 with condition number
% 10^sig.  It also generates the right hand side of a linear system Ax=b
% and an approximate solution xt that is accurate to about 16-sig
% decimal digits.  The linear system is then solved with an underlying
% precision of rho decimal digits and performs four steps of iterative
% refiniment with the residual evaluated in tau-digit decimal floating
% point arithmetic.