Watanabe and Hu Reply
  The article is an reply to comments on the paper [H. Watanabe, S. Yukawa, N. Ito, and C.-K. Hu, Phys. Rev. Lett. vol. 93, 19601 (2004)] by G. Pruessner and N. R. Moloney published in [Phys. Rev. Lett. vo. 95, 258901 (2005)]. In this reply, we also point out that the exponents $a$ and $b$ in the 2004 paper just mentioned can be calculated from mapping functions. 
Hiroshi Watanabe and Chin-Kun Hu