Thread: how to program zipfian distribution

  1. #1
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    how to program zipfian distribution

    The thing is this: A line range is between a and b, in x axis. I have to generate random numbers according to the zipfian distribution(skewed towards a) in that range, but I have not found the way to manipulate a function to do that.

    Some idea?

    Thanks a lot!"!

  2. #2
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  3. #3
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    Wink some code

    now i find some code about zipfian, which gives the range between x1 and x2

    Code:
    double HsubV=0;
    
    void InitZipfHsubV(double p,int V=100) {
    	// calculate the V-th harmonic number HsubV. WARNING: V>1
    	HsubV = 0.0;
    	for (int i=1; i<=V; i++)
    		HsubV += 1.0/pow( (double)i, p); //Hsub=zipfian 1/c
    }
    
    //int ino[105]={0};
    float drd;
    float zipf(float x1, float x2, double p,int V=100) {
       float x,i;
       double r, sum;
    
       do {
    	   // assume InitZipfHsubV called, HsubV known
    	   // faster, no need to compute HsubV every time !
    
    	   drd = drand48();
    	   r=drd*HsubV;
    	   sum=1.0; 
    	   drd = drand48();i=drd;
    	   while (sum<r){
    	      //i++;  //commented by Yufei Tao
    
    		  drd = drand48(); i+=drd+1.0;
    
    	      sum += 1.0/pow( (double)i, p);
    	   }
    
    	   /* i follows Zipf distribution and lies between 1 and V */
    	   /* x lies between 0. and 1. and then between x1 and x2 */
    	   x = ( (float) i - 1. ) / ( (float) V - 1. );
    	   x = (x2 - x1) * x + x1;
    
    	   //if( x > x1 && x < x2 ) ino[int(ceil(i))]++ ;//printf( "i:%f r:%f x:%f\n",i,r,x );
       } while (x < x1 || x > x2);
       return(x);
    }

  4. #4
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    Question i don't know what u mean?

    can u tell me in detail?please

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