implementations of kurtosis

/* Return the kurtosis of values in datalist.
    kurtosis1 implements the formula used by
    MINITAB and MS Excel. */
double kurtosis1(double *datalist, size_t listsize)
{
     int idx;
     double n, mean, sd, t1, t2, t3;

     n = (double)listsize;
     mean = a_mean(datalist, listsize);
     sd = s_stdev(datalist, listsize);
     if(n < 4. || dbl_isequal(sd, 0.0))
     {
         fprintf(stderr, "\nerror: invalid input to kurtosis()\n");
         return 0.0;
     }
     t1 = (n*(n+1))/((n-1)*(n-2)*(n-3));
     t2 = 0.0;
     for(idx = 0; idx < listsize; idx++)
     {
         t2 += pow((datalist[idx] - mean)/sd, 4.);
     }
     t3 = (3.0*((n-1)*(n-1)))/((n-2)*(n-3));

     return (t1 * t2) - t3;
}

/* Return the kurtosis of values in datalist.
    kurtosis2 implements the formula used by NIST Dataplot. */
double kurtosis2(double *datalist, size_t listsize)
{
     int idx;
     double mean, sd, sum;

     mean = a_mean(datalist, listsize);
     sd = s_stdev(datalist, listsize);
     sum = 0.0;
     for(idx = 0; idx < listsize; idx++)
     {
         sum += pow(datalist[idx] - mean, 4.0) / (listsize - 1);
     }

     return sum / pow(sd, 4.0);
}