[求助]Taflove的FDTD书附带程序的问题请教

刚开始学习FDTD，看了Taflove的FDTD书附带程序里的一维FDTD算法，有些不明白的地方，想请教各位，请大家不吝赐教！ E7D DMU  
1。scfact=dt/muz/dx;中的scfact有什么作用？为什么要设这个参数呢，有何实际意义？ FW4 hqgE@  
2.cb=scfact*(dt/epsz/eps/dx)/(1.0+(dt*sig)/(2.0*epsz*eps));中的计算方法为什么是这样的而不是cb=(dt/(epsz*eps))/(1.0+(dt*sig)/(2.0*epsz*eps));后一个是我在课本上找到的公式。为什么会用前一个！ frt?*|:  
=zKp(_[D  
本人很菜，希望高手能耐心赐教，不胜感激！谢谢 yLP0w^Q  
qCMcN<:>  
附上源程序： 6~s,j({^  
%*********************************************************************** [*(MI 9WM  
%     1-D FDTD code with simple radiation boundary conditions Jz6PqU|=  
%*********************************************************************** 7blZAA?-  
% tj0vB]c  
%     Program author: Susan C. Hagness /zWWUl`:  
%                     Department of Electrical and Computer Engineering =[,adB  
%                     University of Wisconsin-Madison v3p..A~XZ.  
%                     1415 Engineering Drive $W2AiE[Wm  
%                     Madison, WI 53706-1691 Q.Acmht#  
%                     608-265-5739 8"@<s?0\"  
%                     hagness@engr.wisc.edu q%"nk  
% SO%5ts  
%     Date of this version:  February 2000 h$!qb'|  
% /D q]=P  
%     This MATLAB M-file implements the finite-difference time-domain *=8)]_=f  
%     solution of Maxwell's curl equations over a one-dimensional space C{D2mSS  
%     lattice comprised of uniform grid cells. ;"3Mm$  
% ,#A,+!4  
%     To illustrate the algorithm, a sinusoidal wave (1GHz) propagating tv0xfAV  
%     in a nonpermeable lossy medium (epsr=1.0, sigma=5.0e-3 S/m) is 1#V0g Q  
%     modeled.  The simplified finite difference system for nonpermeable \?o%<c5{  
%     media (discussed in Section 3.6.6 of the text) is implemented. wcOAyo5(n  
% R8E<;^?j  
%     The grid resolution (dx = 1.5 cm) is chosen to provide 20 nF-FoO98  
%     samples per wavelength.  The Courant factor S=c*dt/dx is set to \yqiv"'  
%     the stability limit: S=1.  In 1-D, this is the "magic time step." u0,~pJvX  
% C9z{8 ;  
%     The computational domain is truncated using the simplest radiation VlEkT9^:  
%     boundary condition for wave propagation in free space: s-*XAnot  
% OjHBzrK  
%                      Ez(imax,n+1) = Ez(imax-1,n) Pzqgg43Xf  
% ru&RL HFV  
%     To execute this M-file, type "fdtd1D" at the MATLAB prompt. \@xnC$dd/  
%     This M-file displays the FDTD-computed Ez and Hy fields at every (#:Si~3  
%     time step, and records those frames in a movie matrix, M, which is Q*wx6Pu8  
%     played at the end of the simulation using the "movie" command. #O~Y[''C5X  
% }8svd#S+  
%*********************************************************************** %/s1ma6q  
clear (mEZ4yM
 
%*********************************************************************** KQqlM  
%     Fundamental constants  u32<=Q[  
%*********************************************************************** ]:njP3r  
cc=2.99792458e8;            %speed of light in free space XEuv aM  
muz=4.0*pi*1.0e-7;          %permeability of free space jC oZm(bi  
epsz=1.0/(cc*cc*muz);       %permittivity of free space U+ 8[Ia(t  
freq=1.0e+9;                %frequency of source excitation bhI8b/  
lambda=cc/freq;             %wavelength of source excitation &.}zZ/  
omega=2.0*pi*freq; |LQmdgVr$  
%*********************************************************************** 97g\nq<  
%     Grid parameters Mf *qr9*  
%*********************************************************************** <[q)2 5RL  
ie=200;                     %number of grid cells in x-direction  4@5<B  
ib=ie+1; ~7m+cWC-+  
dx=lambda/20.0;             %space increment of 1-D lattice 8177x7UG2[  
dt=dx/cc;                   %time step ,kP{3.#Q  
omegadt=omega*dt; f9$98SI  
nmax=round(12.0e-9/dt);     %total number of time steps 7+c@pEU]  
%*********************************************************************** bIH2cJ  
%     Material parameters G$Dg*<  
%*********************************************************************** ~UnfS};
U  
eps=1.0; @f$P*_G   
sig=5.0e-3; q<1@ut  
%*********************************************************************** >
[p+L='  
%     Updating coefficients for space region with nonpermeable media ,"/_G  
%*********************************************************************** <D=%55  
scfact=dt/muz/dx; vL><Y.kOEs  
ca=(1.0-(dt*sig)/(2.0*epsz*eps))/(1.0+(dt*sig)/(2.0*epsz*eps)); TQ BL!w  
cb=scfact*(dt/epsz/eps/dx)/(1.0+(dt*sig)/(2.0*epsz*eps));  A=,
m  
%*********************************************************************** AkF1
Hj  
%     Field arrays 5t PmrWZ  
%*********************************************************************** D H/1
:H  
ez(1:ib)=0.0; Y,a.9AWw)  
hy(1:ie)=0.0; 1/gh\9h  
%*********************************************************************** UeRenp  
%     Movie initialization xj}N;FWo  
%*********************************************************************** eI[z%j[Y*  
x=linspace(dx,ie*dx,ie); Q.N^1?(>k  
subplot(2,1,1),plot(x,ez(1:ie)/scfact,'r'),axis([0 3 -1 1]); +vQyHo  
ylabel('EZ'); YONg1.^!(  
subplot(2,1,2),plot(x,hy,'b'),axis([0 3 -3.0e-3 3.0e-3]); O-7 \qz  
xlabel('x (meters)');ylabel('HY'); (/)JnBy0  
rect=get(gcf,'Position'); h m"B kOA  
rect(1:2)=[0 0]; ]*@7o^4i  
M=moviein(nmax/2,gcf,rect); 5pDxFs=v  
%*********************************************************************** -,rl[1ZYZ  
%     BEGIN TIME-STEPPING LOOP !=-l760  
%*********************************************************************** .`iq+i~  
for n=1:nmax c(~M<nL0  
%*********************************************************************** ~(^
[TuJC  
%     Update electric fields a5)+5  
%*********************************************************************** M,9WF)p)V  
ez(1)=scfact*sin(omegadt*n); zJ\I%7h*  
rbc=ez(ie); uIR_p\)  
ez(2:ie)=ca*ez(2:ie)+cb*(hy(2:ie)-hy(1:ie-1)); .
-r 1.'.A  
ez(ib)=rbc; mF_/Rhu  
%*********************************************************************** BG|Kw)z*KM  
%     Update magnetic fields .OjJK?  
%*********************************************************************** 0 cQf_o  
hy(1:ie)=hy(1:ie)+ez(2:ib)-ez(1:ie); aw,8'N)  
%************************************ .. 0}ZuF.  
&K7g8x"x.  

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你看谁的程序应结合谁的书看，因为各个人编程时离散方程后设置的迭代系数形式上可能不一样。 yeW|Ux:  
这个程序你最好看Allen的第三版的书（第二版）也可以 tkd2AMkh!  
1.是用来归一化电场的一个表示式。第三版P71页（3.37）式。 Y!SD^Ie7!  
2.P72（3.38）和P67（3.31）

呵呵，我以前也被这个问题困惑原来如此，谢谢

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非常感谢herosword！~ K+PzTGWq^  
wq_463 ，我的QQ是15469459！一起学习交流！