[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！ +<&E3Or  
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？ ;:P7}v fz!  
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！ d>UnJ)V}  
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本人很菜，希望高手能耐心赐教，不胜感激！谢谢 cI5N"U@yN  
Q\H_t)-  
附上源程序： {Jrf/p9w  
%*********************************************************************** ]*0(-@  
%     1-D FDTD code with simple radiation boundary conditions 5`"iq "5Cf  
%*********************************************************************** 4bnt=5]  
% $Jcq7E~  
%     Program author: Susan C. Hagness D>P;Izb  
%                     Department of Electrical and Computer Engineering (}G!np  
%                     University of Wisconsin-Madison L/~D<V  
%                     1415 Engineering Drive bV_j`:MD  
%                     Madison, WI 53706-1691 gt'*B5F(  
%                     608-265-5739 C?/r;  
%                     hagness@engr.wisc.edu YUCC*t  
% L${m/@9  
%     Date of this version:  February 2000 Q |%-9^  
% SgiDh dE  
%     This MATLAB M-file implements the finite-difference time-domain rR\;G2
p)  
%     solution of Maxwell's curl equations over a one-dimensional space  m;c3Z-  
%     lattice comprised of uniform grid cells. VrVDm*AGQ  
% q]K'p,'  
%     To illustrate the algorithm, a sinusoidal wave (1GHz) propagating 975 _d_U  
%     in a nonpermeable lossy medium (epsr=1.0, sigma=5.0e-3 S/m) is 6.[)`iF+#  
%     modeled.  The simplified finite difference system for nonpermeable avg4K*
vv  
%     media (discussed in Section 3.6.6 of the text) is implemented. ~Po<(A}`f  
% I`NUurQTX  
%     The grid resolution (dx = 1.5 cm) is chosen to provide 20 cM3jnim  
%     samples per wavelength.  The Courant factor S=c*dt/dx is set to .@@an;C  
%     the stability limit: S=1.  In 1-D, this is the "magic time step." M_Bu,<q^  
% GLCAiSMz[  
%     The computational domain is truncated using the simplest radiation e^zHw^js  
%     boundary condition for wave propagation in free space: "TfI+QgLF  
% tj[c#@[B  
%                      Ez(imax,n+1) = Ez(imax-1,n) ZNi +Aw$u  
% syRN4  
%     To execute this M-file, type "fdtd1D" at the MATLAB prompt. %y
fE7UPS]  
%     This M-file displays the FDTD-computed Ez and Hy fields at every mg`j[<wp  
%     time step, and records those frames in a movie matrix, M, which is RpYcD  
%     played at the end of the simulation using the "movie" command. Hte[TRbM  
% e9 *lixh  
%*********************************************************************** k=`$6(>Fz  
clear 6AAswz'$P  
%*********************************************************************** G{+2xN a(  
%     Fundamental constants j1A|D   
%*********************************************************************** P].eAAXnP  
cc=2.99792458e8;            %speed of light in free space Fwb5u!_,  
muz=4.0*pi*1.0e-7;          %permeability of free space UU[H@ym
#  
epsz=1.0/(cc*cc*muz);       %permittivity of free space 2L:$aZ  
freq=1.0e+9;                %frequency of source excitation \9w~pO  
lambda=cc/freq;             %wavelength of source excitation 0'`S,  
omega=2.0*pi*freq; w//omF'`  
%*********************************************************************** -G-3q
6A  
%     Grid parameters 1DqX:WM6  
%*********************************************************************** *jE;9^  
ie=200;                     %number of grid cells in x-direction t!jYu<P  
ib=ie+1; Kk=L
XmL2  
dx=lambda/20.0;             %space increment of 1-D lattice o5SQ1;`   
dt=dx/cc;                   %time step <[ZI.+_Wt  
omegadt=omega*dt; z6I%wh  
nmax=round(12.0e-9/dt);     %total number of time steps xz8G}Ku  
%*********************************************************************** _lX8K:C(  
%     Material parameters P_&p=${  
%*********************************************************************** DHv2&zH  
eps=1.0; 6Cv.5Vhx  
sig=5.0e-3; pw\P<9e=  
%*********************************************************************** &))\2pl  
%     Updating coefficients for space region with nonpermeable media RJhK$\  
%*********************************************************************** -%,"iaO  
scfact=dt/muz/dx; P\AqpQv  
ca=(1.0-(dt*sig)/(2.0*epsz*eps))/(1.0+(dt*sig)/(2.0*epsz*eps)); N'QqJe7Z  
cb=scfact*(dt/epsz/eps/dx)/(1.0+(dt*sig)/(2.0*epsz*eps)); 6Hk="$6K  
%*********************************************************************** QD$Gw-U-l=  
%     Field arrays 'C
^;OjAg  
%*********************************************************************** i$C-)d]  
ez(1:ib)=0.0; {~_Y _-  
hy(1:ie)=0.0; dw9Tf^V  
%*********************************************************************** m'bi\1Q  
%     Movie initialization L=]p_2+  
%*********************************************************************** cI:-Z{M7z  
x=linspace(dx,ie*dx,ie); &iBNO,v  
subplot(2,1,1),plot(x,ez(1:ie)/scfact,'r'),axis([0 3 -1 1]); {n&Uf{  
ylabel('EZ'); n1,S_Hs  
subplot(2,1,2),plot(x,hy,'b'),axis([0 3 -3.0e-3 3.0e-3]); JRY_nX  
xlabel('x (meters)');ylabel('HY'); [9AM\n>g  
rect=get(gcf,'Position'); 'mE^5K  
rect(1:2)=[0 0]; h&`y$Jj  
M=moviein(nmax/2,gcf,rect); 0e16Ow6\!1  
%*********************************************************************** '1-maM\r  
%     BEGIN TIME-STEPPING LOOP D:9 2\l  
%*********************************************************************** @^&7$#jq%  
for n=1:nmax m(_9<bc>  
%*********************************************************************** ,F9nDF@)  
%     Update electric fields ~x#vZ=]8  
%*********************************************************************** kAo.C Nj7  
ez(1)=scfact*sin(omegadt*n); KP{3iUqvO  
rbc=ez(ie); "(f`U.  
ez(2:ie)=ca*ez(2:ie)+cb*(hy(2:ie)-hy(1:ie-1)); r[pF^y0   
ez(ib)=rbc; 64umul  
%*********************************************************************** {$33B'wk  
%     Update magnetic fields uokc:D  
%*********************************************************************** %j5ywr:  
hy(1:ie)=hy(1:ie)+ez(2:ib)-ez(1:ie); <<,>S&/  
%************************************ .. ?:uNN  
RV;!05^<  

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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。 :kG)sw7  
这个程序你最好看Allen的第三版的书（第二版）也可以 1m)M;^_  
1.是用来归一化电场的一个表示式。第三版P71页（3.37）式。 Bm/
YgQi  
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

楼主留个qq咱们可以多交流

非常感谢herosword！~ 3$/ 4wH^  
wq_463 ，我的QQ是15469459！一起学习交流！