对称振子的电流分布图

[strelizia]

求助，电流分布图只有正半轴，没有负半轴。不知道该怎么修改，思路见下。
clear all;
clc;
clf;
tic; %计时
lambda=1;
N=31;a=0.0000001;%已知天线和半径
ii=0;
for h=0.2:0.1:0.9
ii = ii+1;
L=h*lambda;
len=L/N;%将线分成奇数段,注意首末两端的电流为0
e0=8.854e-012;u0=4*pi*10^(-7);k=2*pi/lambda;
c=3e+008;w=2*pi*c;%光速,角频率
ata=sqrt(u0/e0);
z(1)=-L/2+len/2;
for n=2:N
z(n)=z(n-1)+len;
end
for m=1:N
for n=1:N
if (m==n)
p(m,n)=log(len/a)/(2*pi)-j*k*len/4/pi;
else
r(m,n)=sqrt((z(m)-z(n))^2+a^2);
p(m,n)=len*exp(-j*k*r(m,n))/(4*pi*r(m,n));
end
end
end
for m=1:N
q(m)=cos(k*z(m));
s(m)=sin(k*z(m));
t(m)=sin(k*abs(z(m)))/(j*2*ata);
end
pp=p(N+1:N^2-N);
pp=reshape(pp,N,N-2);
mat=[pp,q',s'];%构造矩阵
I=mat\t';
II=[0;I(1:N-2);0];%加上两端零电流
Current=abs(II);
x=linspace(-L/2,L/2,N);
figure(1);
string=['b','g','r','y','c','k','m','r'];
string1=['ko','bo','yo','co','mo','ro','go','bo'];
plot(x,Current,string(ii),'linewidth',1.3);
xlabel('L/\lambda'),ylabel('电流分布');
grid on
hold on
%legend('L=0.1\lambda','L=0.3\lambda','L=0.5\lambda','L=0.7\lambda','L=0.9\lambda','L=1.1\lambda','L=1.3\lambda','L=1.5\lambda')
legend('L=0.1\lambda','L=0.3\lambda','L=0.5\lambda','L=0.7\lambda','L=0.9\lambda','L=1.1\lambda','L=1.3\lambda','L=1.5\lambda')
Zmn=1/I((N+1)/2);%%%%%%V=1v
theta=linspace(0,2*pi,360);
运行结果如图所示
https://www.ilovematlab.cn/forum.php?mod=image&aid=288880&size=300x300&key=c67e83873fabaa18&nocache=yes&type=fixnone
按道理来说应该是这样子的
https://www.ilovematlab.cn/forum.php?mod=image&aid=288881&size=300x300&key=b78fe70a464dd25e&nocache=yes&type=fixnone
请问该怎么修改呢？有劳大佬指教了。
matlab2019a Win10 1903