A trick: why \hat\gamma < \gamma (=3) in [1=arXiv:cond-mat/0106096]?
  In this paper, first a theorem on the partial sum of a particular series is given. Then, based on it, the origin of obvious simulation deviation from theory is explained: i) why the numerically estimated \hat\gamma (degree exponent) in [1=arXiv:cond-mat/0106096] is always smaller than \gamma (=3) that is predicted by theory; ii) and why \hat\gamma rises monotonically as m (the links added at each step in Barabasi-Albert (BA) model [1]) increases. Strictly, it declares such errors are basically from the inconsistence of simulation with the theoretical model, which is caused by an additional incompatible condition used in simulation. In addition, noticing the evolving differences between the initial m_0 nodes and those after, we correct the derived BA model which unfairly omitted such differences. 
Wuhua Hu