octave> m=readpgm('mars.pgm');
magic number = P2
rows = 383 cols = 279
grey levels = 255
octave> mh=histogram(m,256);
octave> mp=mh/sum(mh);
octave> plot(0:255,mp);



octave> mc=cdf(mp); # you write cdf
octave> plot(0:255,mc);



octave> mi=icdf(mp,1000); # you write icdf
octave> plot((1:1000)/1000,mi);



octave> p=exp(-(0:255).^2/1000); 
octave> p=p/sum(p);
octave> b=rand2(p,64); # you write rand2
octave> bh=histogram(b,256)
octave> bp=bh/sum(bh);
octave> mplot(0:255,p,0:255,bp);