baseball.m

一些常被用于教学或者参考的概率论的实例的源代码

%baseball.m/created by PJNahin for "Duelling Idiots"(10/16/98)
%This m-file calculates and plots (as a function of p) the ratio
%of the probabilities of a team winning at least 81p games out of
%81 games to the probability of winning at least 162p games out
%of 162 games, where p is the probability of winning any individual
%game.
%
%
res=input('Resolution of p = ')
clear x
clear ratio
for p=res:res:1-res
   if 81*p==floor(81*p)    %is 81p an integer? if yes then s81=81*p;
      s81=81*p;            %if no, use floor to round DOWN to nearest
   else                    %integer and add one (e.g., "at least 17.3
      s81=floor(81*p)+1;   %games" means "at least 18 games).
   end
   if 162*p==floor(162*p)  %ditto for s162;
      s162=162*p;
   else
      s162=floor(162*p)+1;
   end
   sumnum=0;               %form the numerator sum;
   for k=s81:81
      bc=binomial(81,k);   %See Problem 6;
      sumnum=sumnum+bc*(p^k)*((1-p)^(81-k));
   end
   sumden=0;               %form the denominator sum;
   for k=s162:162
      bc=binomial(162,k);
      sumden=sumden+bc*(p^k)*((1-p)^(162-k));
   end
   index=round(p/res);
   index                   %display current value on screen
                           %to prevent boredom!
 ratio(index)=sumnum/sumden;
 x(index)=p;
end
plot(x,ratio)
grid
title('Fig.7.1-Ratio of Probabilities of Winning At Least np Games Out of n, n=81/np=162')
xlabel('p, probability of winning any individual game')
ylabel('ratio')
figure(1)