code: public static double SymmetricChiSquareDivergence(double[] p, double[] q) {
          double r = 0;
          for (int i = 0; i < p.length; i++) {
              double den = p[i] * q[i];
              if (den != 0) {
                  double p1 = p[i] - q[i];
                  double p2 = p[i] + q[i];
                  r += (p1 * p1 * p2) / den;
              }
          }
  
          return r;
      }
docs: Gets the Symmetric Chi-square divergence.
  
  @param p P vector.
  @param q Q vector.
  @return The Symmetric chi-square divergence between p and q.