code: public void setG(double G)
      {
          if(G < 1 || Double.isInfinite(G) || Double.isNaN(G))
              throw new IllegalArgumentException("G must be in [1, Infinity), not " + G);
          this.G = G;
      }
docs: Sets the sparsification parameter G. Increasing G reduces the number of
  updates to the model, which increases sparsity but may reduce accuracy.
  Decreasing G increases the update rate reducing sparsity. The original
  paper tests values of G &isin; {1, 2, 4, 10}
  @param G the sparsification parameter in [1, &infin;)