function retval = quadfn(x)
% usage:  y = quadfn(x)
% description: Returns value of quadratic test function
% of the form Q(x) = 0.5*x'*A*x - b*x
% where A is symmetric, A and b are globals defined
% outside this function.  This is really a placeholder
% for linear system solving.

global quadA;
global quadb;

% no bulletproofing
retval = 0.5*x'*quadA*x - quadb'*x;