MATLAB 二进制转换四进制时出错的问题

ytm

请大佬看看这段程序
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function [y,yn]=two2four(x,m)
* V; @% E, X9 q' O%二进制转换成四进制
syms x
2 M) u  O" |4 W: \, ]0 {( [, X$ qT=[0 1;3 2];
n=length(x);
ii=1;
; S& I4 z# ~! M0 ]7 ?% n, T& dfor i=1:2:n-1;
    xi=x(i:i+1)+1;
    yn(ii)=T(xi(1),xi(2));
    ii=ii+1;
end
. b* v6 p. |5 k+ oyn=yn-1.5;
y=yn;
6 f2 Z) t% G0 V9 @. g; ^5 Ufor i=1:m-1;
# K: f7 z$ e4 T+ J. x    y=[y;yn];
8 `4 G5 p/ J9 t- Aend
6 f5 D# ]# y2 [+ ^7 F5 ?y=y(';
运行显示
??? Undefined function or variable "yn".
Error in ==> two2four at 12
yn=yn-1.5;

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fawa

yn=yn-1.5;这句代码有错，左侧的yn=右侧的yn-1.5
但右侧的yn在前面的代码中未定义，所以报错，定义一下就好