[求助]程序出错，不知怎么改

[kobybry_cn]

L=201;
axis([-L,L,0.0001,2*pi]);
set(gcf,'color','w');
axis off;
a=2/3;
x=[-L,L];
y=linspace(0.0001,2*pi,2*L)
[X,Y]=meshgrid(x,y);
Z=X+i*Y;
W=exp(Z);
l=0.001;
f_l(W)=W.^(1-a).*((1+l)\(2*W).*(1+W).*[1+W+sqrt(W.^2+1-2*W*(1-l)/(1+l))]-1).^a;
f_l,theta(W)=exp(i*theta)*f_l(exp(-i*theta)*W);
Z=W;
while k>=1&&k<=2000
theta=rand*2*pi;
dfZ=diff(f_l,theta(W),esp(theta));
jd(Z)=(abs(dfZ))^(-2);
l=l_0*jd(Z);
Z=Z(f_l,theta(W));
plot(Z);
k=k+1;
end
运行之后总是出同样的错误提示??? Subscript indices must either be real positive integers or logicals.

Error in ==> D:\MATLAB6p5\work\dla.m
On line 12 ==> f_l(W)=W.^(3-a).*((1+l)\(2*W).*(1+W).*[1+W+sqrt(W.^2+1-2*W*(1-l)/(1+l))]-1).^a;
请大家帮忙看看到底哪里不对啊