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%求解Lame波反对称部分的模态A2 
format long 
syms c;   %定义速度c为符号函数 
kh=6.5  %k为波数,h为总的板厚 
cd=5790;cs=3200; %cd为纵波波速,cs为横波波速 
y1=-4*tan(kh/2*((c/cs)^2-1)^(1/2))*((c/cd)^2-1)^(1/2)*((c/cs)^2-1)^(1/2); 
y2=(2-(c/cs)^2)^2*tan(kh/2*((c/cd)^2-1)^(1/2)); 
c=[5790;6100]; 
eps=1e-12; 
xx=[]; 
for i=2:2 
    a=c(i-1);b=c(i); 
    c=(a+b)/2; 
    while (subs(y1-y2)~= 0) & ((b-a)>eps) 
        c=(a+b)/2; 
        fa=-4*tan(kh/2*((a/cs)^2-1)^(1/2))*((a/cd)^2-1)^(1/2)*((a/cs)^2-1)^(1/2)-(2-(a/cs)^2)^2*tan(kh/2*((a/cd)^2-1)^(1/2)); 
        fb=-4*tan(kh/2*((b/cs)^2-1)^(1/2))*((b/cd)^2-1)^(1/2)*((b/cs)^2-1)^(1/2)-(2-(b/cs)^2)^2*tan(kh/2*((b/cd)^2-1)^(1/2)); 
        fy=-4*tan(kh/2*((c/cs)^2-1)^(1/2))*((c/cd)^2-1)^(1/2)*((c/cs)^2-1)^(1/2)-(2-(c/cs)^2)^2*tan(kh/2*((c/cd)^2-1)^(1/2)); 
        if fa*fy < 0 
            b=c; 
        else 
            a=c; 
        end 
    end 
    xx=[xx;c] 
    m=subs(y1-y2) 
end