tree.m

这里面有很多有用的东东

function tree(n)
%TREE
%Draws a fractal tree.
%Calling format: tree(n), where n is desired # iterations.

%Copyright Gareth Williams, Stetson University 
[e-mail], http://www.stetson.edu/~gwilliam
%Accompanies "Linear Algebra with Applications" by Gareth Williams

disp(' ')
disp('   - To Stop At Any Time -') 
disp('    command period (Mac)')
disp('       Ctrl C (IBM)')
disp(' ')
disp('- press Enter to get picture - ')
disp(' ')
pause

clf;

A=[.42 .42;-.42 .42];E=[0;.2];
B=[.42 -.42;.42 .42];F=[0;.2];
C=[.1 0;0 .1];G=[0;.2];
D=[0 0;0 .5];H=[0;0];

%accumulated probabilities
P=[.4 .8 .95 1];

%Plot the points generated by the affine transforms

X=[0 0];Y=[0 0];           % initialize variables
Y1 = zeros(1,n); Y2 = Y1;  % pre-allocate vectors
figure(gcf)

%Ranges of x & y axes
V=[-.4 .5 0 .5];
axis(V); axis(axis);
hold on

for i=1:n,
 pk=rand;
 if pk<=P(1)
   Y(1) = A(1,1)*X(1)+A(1,2)*X(2)+E(1);
   Y(2) = A(2,1)*X(1)+A(2,2)*X(2)+E(2);
  elseif pk<=P(2)
   Y(1) = B(1,1)*X(1)+B(1,2)*X(2)+F(1);
   Y(2) = B(2,1)*X(1)+B(2,2)*X(2)+F(2); 
  elseif pk<=P(3) 
   Y(1) = C(1,1)*X(1)+C(1,2)*X(2)+G(1);
   Y(2) = C(2,1)*X(1)+C(2,2)*X(2)+G(2);
  elseif pk<=P(4)
   Y(1) = D(1,1)*X(1)+D(1,2)*X(2)+H(1);
   Y(2) = D(2,1)*X(1)+D(2,2)*X(2)+H(2);
 end

 clear X;
 X=Y;
 
 %save coordinate values for plotting
 Y1(i) = Y(1);
 Y2(i) = Y(2);

 % If you wanted to plot one point at a time
 % and not have the screen flicker, use 'XOR' mode.
 plot(Y(1),Y(2),'.','erasemode','xor');
 drawnow
 clear Y;
end

%%% Doing all of the plotting at the end is much faster %%%
% plot(Y1,Y2,'.')
% Ranges of x & y axes
% V=[-4 6 -1 12];
% axis(V);

hold off