[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！ hb!
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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？ vfXJYw+6_  
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！ {{E jMBg{  
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本人很菜，希望高手能耐心赐教，不胜感激！谢谢 QSmJ`Bm  
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附上源程序：
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%*********************************************************************** F;a3  
%     1-D FDTD code with simple radiation boundary conditions JmjxGcG  
%*********************************************************************** BVAr&cu  
% Vr\Q`H.  
%     Program author: Susan C. Hagness -,/3"}<^78  
%                     Department of Electrical and Computer Engineering ,F}r@  
%                     University of Wisconsin-Madison !2tw,QM
  
%                     1415 Engineering Drive b8cVnP  
%                     Madison, WI 53706-1691  0dh#/  
%                     608-265-5739 eKJ:?Lxv;  
%                     hagness@engr.wisc.edu Tc,$TCF  
% Bhx<g&|j  
%     Date of this version:  February 2000 o4'W
r  
% /=trj5h  
%     This MATLAB M-file implements the finite-difference time-domain Oc^m_U8>^  
%     solution of Maxwell's curl equations over a one-dimensional space ;[caiMA-  
%     lattice comprised of uniform grid cells. &GU@8  
% \kk!Dz*H  
%     To illustrate the algorithm, a sinusoidal wave (1GHz) propagating bx7\QU+  
%     in a nonpermeable lossy medium (epsr=1.0, sigma=5.0e-3 S/m) is F8 ?uQP8  
%     modeled.  The simplified finite difference system for nonpermeable hpjUkGm5  
%     media (discussed in Section 3.6.6 of the text) is implemented. ~B*~'I9b*  
% <p)Z/  
%     The grid resolution (dx = 1.5 cm) is chosen to provide 20 ixzTJ]yu  
%     samples per wavelength.  The Courant factor S=c*dt/dx is set to <c\]Ct  
%     the stability limit: S=1.  In 1-D, this is the "magic time step." -s89)lUkS  
% =Pj@g/25u  
%     The computational domain is truncated using the simplest radiation >3+FZ@.iT  
%     boundary condition for wave propagation in free space: @9<S*  
% YJc%h@_=]  
%                      Ez(imax,n+1) = Ez(imax-1,n) a6qwL4  
% lDlj+fK  
%     To execute this M-file, type "fdtd1D" at the MATLAB prompt. = uk`pj  
%     This M-file displays the FDTD-computed Ez and Hy fields at every L^jaBl  
%     time step, and records those frames in a movie matrix, M, which is yP%o0n/"x  
%     played at the end of the simulation using the "movie" command. u/#&0_ P  
% u6p5:oJj,  
%***********************************************************************  Lxz  
clear K{N%kk%F  
%*********************************************************************** (tpof 5a  
%     Fundamental constants e^Aa!  
%*********************************************************************** 5=m3J!?  
cc=2.99792458e8;            %speed of light in free space XW^8A77H  
muz=4.0*pi*1.0e-7;          %permeability of free space v}&#f&q!  
epsz=1.0/(cc*cc*muz);       %permittivity of free space :Dt\:`(r'  
freq=1.0e+9;                %frequency of source excitation bk
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lambda=cc/freq;             %wavelength of source excitation gjQ=8&i  
omega=2.0*pi*freq; lc"qqt  
%*********************************************************************** Y!;gQeC  
%     Grid parameters p6 <}3m$  
%*********************************************************************** 9,w}Xe=C  
ie=200;                     %number of grid cells in x-direction Ny B&uf  
ib=ie+1; LjC6?a_?l  
dx=lambda/20.0;             %space increment of 1-D lattice 0w'|d@*wV  
dt=dx/cc;                   %time step `LE^:a:8,  
omegadt=omega*dt; ) (+)Q'*  
nmax=round(12.0e-9/dt);     %total number of time steps )X~#n  
%*********************************************************************** ?-d Ain1w  
%     Material parameters QQT G9s  
%*********************************************************************** PlF!cr7:4  
eps=1.0; :;q>31:h  
sig=5.0e-3;  A<2I!  
%*********************************************************************** s><IykIi  
%     Updating coefficients for space region with nonpermeable media .
E#<fz  
%*********************************************************************** XL&hs+Y  
scfact=dt/muz/dx; @Mzz2&(dU  
ca=(1.0-(dt*sig)/(2.0*epsz*eps))/(1.0+(dt*sig)/(2.0*epsz*eps)); 2q/nAQ+  
cb=scfact*(dt/epsz/eps/dx)/(1.0+(dt*sig)/(2.0*epsz*eps)); N:OD0m%`)  
%*********************************************************************** 3y/1!A3  
%     Field arrays &7fY_~)B  
%*********************************************************************** _ r~+p  
ez(1:ib)=0.0; m:b^,2"g  
hy(1:ie)=0.0; tnN'V  
%*********************************************************************** (lieiye^  
%     Movie initialization mZ~mf->%  
%*********************************************************************** 2|$lk8/,  
x=linspace(dx,ie*dx,ie); ,zG<7~m  
subplot(2,1,1),plot(x,ez(1:ie)/scfact,'r'),axis([0 3 -1 1]); 8znj~7}#  
ylabel('EZ'); \m%J`{Mt  
subplot(2,1,2),plot(x,hy,'b'),axis([0 3 -3.0e-3 3.0e-3]); `(!W s\:  
xlabel('x (meters)');ylabel('HY'); O1|B3M[P  
rect=get(gcf,'Position'); ot]>}[  
rect(1:2)=[0 0]; x3gwG)Sf  
M=moviein(nmax/2,gcf,rect); .r7D)xNa@  
%*********************************************************************** XynU/Go,  
%     BEGIN TIME-STEPPING LOOP Zo
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%*********************************************************************** ;x,+*%  
for n=1:nmax )-)ss"\+Ju  
%*********************************************************************** bd}
r#^'K  
%     Update electric fields T.J`S(oI  
%*********************************************************************** pn|p
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ez(1)=scfact*sin(omegadt*n); y#&$f  
rbc=ez(ie); \y[Bu^tk  
ez(2:ie)=ca*ez(2:ie)+cb*(hy(2:ie)-hy(1:ie-1)); ^v ]UcnB0  
ez(ib)=rbc; @X K
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%*********************************************************************** N?\bBt
@  
%     Update magnetic fields 1!X1wCT  
%*********************************************************************** 4}+xeGA$  
hy(1:ie)=hy(1:ie)+ez(2:ib)-ez(1:ie); fE
'-.nA+  
%************************************ .. ^GE^Q\&D&  
qo)Q}0  

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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。 Y0@'za^y  
这个程序你最好看Allen的第三版的书（第二版）也可以 )?F$-~7  
1.是用来归一化电场的一个表示式。第三版P71页（3.37）式。 o G(0i  
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！~ 9#Aipu\  
wq_463 ，我的QQ是15469459！一起学习交流！