matlab曲线绘图

matlab中曲线绘图，报错

```c
xx=[];
num=[];
eng=[];
oth=[];
k=1;
e=1;
m=1;
for i=1:10

a=input('请输入：','s');
if ((a>='0'&&a<='9'))
    num(k)= str2double(a);
    k=k+1;
elseif ((a >= 'A' && a <= 'Z')||(a >= 'a' && a<= 'z'))
    eng(e)=a;
    e=e+1;
else
    oth(m)=a;
    m=m+1;
end
xx(i)=a;

end
disp(num);
fprintf('%s\n',eng,oth)
geshu=length(num(:));
if (geshu>3)
mas=max(num);
Y_0=poly2sym(num./mas);
Y=Y_0.*mas;
x=1:0.01:20;
plot(x,Y);
else
disp(1);

end

报错显示：

哪位大神能帮忙看一看，孩子的考试题，救救孩子吧！
感谢大佬！