function ball(p);
% BALL   ball(p)
% draws unit ball of  ||  ||_p  for  0 < p < infty

plot([0  0],[-1.5 1.5],'k','LineWidth',1.5), hold % y xis
plot([-1.5 1.5],[0  0],'k','LineWidth',1.5) % x axis
topx=-1:.01:1; topy=(ones(1,201)-abs(topx).^p).^(1/p);
botx=.99:-.01:-1; boty=-(ones(1,200)-abs(botx).^p).^(1/p);
fill([topx botx],[topy boty],'k','FaceAlpha',0.5,'LineWidth',4)
axis equal, axis([-1.5 1.5 -1.5 1.5]) % make x, y equal
set(gca,'XTick',[]), set(gca,'YTick',[]), hold off