randncond.m

有趣的可视的数值方法 出自网站http://www.mathworks.com/moler

% RANDNCOND  Condition of random matrices

nmax = 100;
n = 2:nmax;
kappalo = n.^(1/2);
kappahi = 500*n.^3;

shg
clf reset
h = loglog(n,[kappalo; kappahi],'-',nmax,NaN,'.');
set(h(1:2),'color',[0 2/3 0]);
set(gca,'xtick',[2:2:10 20:20:nmax])
kappamax = 1.e6;
axis([2 nmax 2 kappamax])
stop = uicontrol('pos',[20 10 40 25], ...
   'style','toggle','string','stop','value',0);

h = h(3);
set(h,'erasemode','none','color','blue')
while get(stop,'value') ~= 1
   n = ceil(rand*nmax);
   A = randn(n,n);
   kappa = condest(A);
   set(h,'xdata',n,'ydata',kappa)
   drawnow
end

set(stop,'val',0,'string','close','callback','close(gcf)')