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%  exa040601cd.m,  for  example 4.6.1 and fig 4.6.1(c)和(d) 
%  BJ分布在四个域内的形状; 
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clear; 
 
n=64; 
for t=1:n; 
   for f=1:n; 
      tt=t-n/2; 
      ff=f-n/2; 
      if abs(ff)>=2*abs(tt) 
         g(t,f)=2*pi; 
      else 
         g(t,f)=0; 
      end 
      if ff~=0 
         g(t,f)=g(t,f)/abs(ff); 
         end 
   end 
end 
t=-n/2+1:n/2; 
f=-n/2+1:n/2; 
subplot(223) 
surfl(t,f,rot90(g),[-37,5,60]); 
subplot(224) 
surfl(t,f,rot90(g),[-37,5,60]);