在 MATLAB 中计算符号表达式时除以零错误

Question

clear all

syms s w 

G = 1/((s)*(s+1)*(s+2)); %transfer function
G_w = subs(G,s,j*w); 
W= [-100:0.01:100]; %[min_range:step size:max_range]
nyq = eval(subs(G_w,w,W)); 

x = real(nyq)
y = imag(nyq)

plot(x,y)

我似乎无法运行这段代码，它一直在第 100++ 行显示错误，而我只有不到 20 行。

Error using symengine (line 59)
Division by zero.
Error in sym/subs>mupadsubs (line 139)
G = mupadmex('symobj::fullsubs',F.s,X2,Y2);
Error in sym/subs (line 124)
    G = mupadsubs(F,X,Y);
Error in nyquist2 (line 8)
nyq = eval(subs(G_w,w,W)); %replace W with w in equation G_w

这是显示的错误，任何专家都可以帮助我吗？

Answer 1

错误是因为您正在G_w使用数组进行计算，W并且该数组包含0导致除以零的值，因此错误。

使用 symengine 时出错（第 59 行）
除以零。

你能做些什么来解决这个问题，是替代0在W用eps。

% Replace zeros with epsilon
W(W == 0) = eps;

nyq = eval(subs(G_w,w,W)); 

x = real(nyq)
y = imag(nyq)

plot(x,y)

作为一个侧面说明，其误差不抱怨与线100+的问题你的代码，而是堆栈跟踪，指出错误竟源于内部的功能，我们在调用

堆栈跟踪从发生错误的位置到您调用以创建它的代码排序

Error using symengine (line 59)             <--- WHERE THE ERROR HAPPENED
Division by zero.                           <--- THIS IS THE ERROR MESSAGE

Error in sym/subs>mupadsubs (line 139)      <--- THIS FUNCTION CALLED symengine
G = mupadmex('symobj::fullsubs',F.s,X2,Y2); <--- THIS IS THE LINE THAT CALLED symengine

Error in sym/subs (line 124)                <--- THIS FUNCTION CALLED mupadsubs
G = mupadsubs(F,X,Y);                       <--- THIS IS THE LINE THAT CALLED mupadsubs

Error in nyquist2 (line 8)                  <--- THIS FUNCTION (YOURS) CALLED subs
nyq = eval(subs(G_w,w,W))                   <--- THIS IS THE LINE THAT CALLED subs