function [] = phallus(l)
%
% PHALLUS
%     
%     The phallus(l) command constructs a 3-D rendition of
%  "The Little Brain" with total length as specified in l.
%  Phallus invoked with no arguments uses the default length
%  of 6.
%

if nargin == 0,
   l=6;,
end

% set up mesh and radius matrices

x=-.3:.01:.3;
[X,Y]=meshgrid(x);
r1=(X.^2 + Y.^2).^.5;
r2=((X+.17).^2+(Y+.17).^2).^.5;
r3=((X+.17).^2+(Y-.17).^2).^.5;

% calculate "pencil"
z1=(sinc(pi/.14*r1)).^2;



% claculate "erasers"

z2=(.03-r2.^2).^.5;
[n,m]=find(r2>=.1732);
for i=1:length(n),
   z2(n(i),m(i))=0;,
end
z2=1.8*real(z2);

z3=(.03-r3.^2).^.5;
[n,m]=find(r3>=.1732);
for i=1:length(n),
   z3(n(i),m(i))=0;,
end
z3=1.8*real(z3);

% scale the whole "thing"

z = l*z1 + (l/2+3)*z2 + (l/2+3)*z3;

%  plot "it"

surf(X,Y,z)

% Shade appropriately

map = colormap;
colormap([map(:,3) map(:,1) map(:,1)]);

% Print positive message

title('Have a Nice Day!')