onedwalk.m

一些常被用于教学或者参考的概率论的实例的源代码

%spider.m/created by PJNahin for "Dueling Idiots"(1/10/99)
%This m-file simulates the one-dimensional, symmetrical walk
%with an absorbing barrier at x = 3.
%
rand('state',100*sum(clock))        %new seed for generator;
web1=[1;0;2;2];                     %input web as column vectors;
web2=[3;0;1;2];
web3=[0;0;4;3];
web=[web1 web2 web3];               %construct web from vectors;
d=zeros(1,100);                     %initialize duration vector;
for walks=1:10000
   position=1;                      %put spider at starting position;
   steps=0;                         %initialize number of steps;
   while position~=2                %if fly not yet reached, then ...
      choices=web(position,1);      %how many choices for next step?
      choice=floor(choices*rand)+2; %make a choice;
      position=web(position,choice);%move to new position;
      steps=steps+1;                %up-date number of steps;
   end
   d(steps)=d(steps)+1;             %fly reached, so up-date
end                                 %duration vector;
average=0;                          %compute the average number of
for i=1:50                          %steps to reach the fly;
   average=average+i*d(i);
end
average/10000
plot(d)                             %plot duration vector;
title('Distribution of Walk Durations')
xlabel('number of steps')
ylabel('number of walks')
figure(1)