改程序是计算出金属表面等离子体直波导的有效折射率随波长和传输长度随波的两色散曲线，另外给定Drude-Lorentzia模型参数给定后，还可以求解介电常数以及画出相应实部和虚部的曲线-This programer is used to calculate Ag relative dielectric constant accroding to the Drude-Lorentzia and sovle the transcendental equation for even illu