4

I'm using LaTeX to write my paper and every equation needs to be numbered, so I use the equation environment. However, it fails to compile.

\documentclass[UTF8]{ctexart}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{epstopdf}
\begin{document}
\begin{equation}
\[
\begin{bmatrix}
    L_{a1} & 0 \\
    0 & L_{a2} 
\end{bmatrix}
 \begin{bmatrix}
    I_{a1}  \\
    I_{a2}
\end{bmatrix}
+
 \begin{bmatrix}
    R_{a1} & 0 \\
    0 & R_{a2} 
\end{bmatrix}
 \begin{bmatrix}
    I_{a1}  \\
    I_{a2}
\end{bmatrix}
+
 \begin{bmatrix}
    K_{e1} & 0 \\
    0 & K_{e2} 
\end{bmatrix}
 \begin{bmatrix}
    $theta_1$ \\
    $theta_2$
\end{bmatrix}
=
 \begin{bmatrix}
    V_{a1} \\
    V_{a2} 
\end{bmatrix}
\]
\end{equation}
\end{document}

So my question is: how to revise it? In addtion, I would like to know why the math expression that follows is wrong:

$$ B = \frac{J_2}{N_1 N_2}+\frac{m_2 r_2^2}{4 N_1 N_2}+\frac{m_2 r_1 r_2}{2 N_1 N_2} cos(\frac{\theat_{m2}}{N_2}) $$
$$ C = \frac{-m_2 r_1 r_2}{N_1 N_2}(\frac{\theat_{m1} \theat_{m2}}{N_1}+\frac{\theat_{m2}^2}{2 N_2}) sin\frac{\theat_{m2}}{N_2} $$
$$ D = J_{m1} +\frac{J_2}{N_2^2}+\frac{m_2 r_2^2}{4 N_2^2} $$
$$ E = \frac{J_2}{N_1 N_2}+\frac{m_2 r_2^2}{4 N_1 N_2}+\frac{m_2 r_1 r_2}{2 N_1 N_2} cos(\frac{\theat_{m2}}{N_2}) $$

LaTeX gives the information:

Undefined control sequence. [..._2}{2 N_1 N_2} cos(\frac{\theat_{m2}}{N_2}]
  • 6
    \theta not \theat. Also you don't need \[ \] inside equation environment. – Sigur Jan 7 '14 at 15:44
  • 5
    And for the last bit, don't use $$ ... $$. See e.g. Why is \[ … \] preferable to $$? – Torbjørn T. Jan 7 '14 at 15:47
  • 3
    Also remove $ from inside bmatrix (you are already in math mode). Also you probably want \theta and not theta – karlkoeller Jan 7 '14 at 15:48
  • 1
    Since you're just starting to learn LaTeX I recommend that you write your math just a little bit at a time, compiling often. That way your mistakes will show up just one at a time and will be easier to find and fix. When you're stuck after trying, ask here, one question at a time. – Ethan Bolker Jan 7 '14 at 16:21
5

The following code should work. Changes:

  • deleted \[ in line 8
  • deleted \] in line 40
  • deleted $ in lines 32 and 33 -> you're already in a math environment, so you don't need to mark this as a math environment by using $ .. $
  • added \ in front of theta in lines 32 and 33

    \documentclass[UTF8]{ctexart}
    \usepackage{amsmath}
    \usepackage{amssymb}
    \usepackage{graphicx}
    \usepackage{epstopdf}
    \begin{document}
    \begin{equation}
    \begin{bmatrix}
        L_{a1} & 0 \\
        0 & L_{a2} 
    \end{bmatrix}
     \begin{bmatrix}
        I_{a1}  \\
        I_{a2}
    \end{bmatrix}
    +
     \begin{bmatrix}
        R_{a1} & 0 \\
        0 & R_{a2} 
    \end{bmatrix}
     \begin{bmatrix}
       I_{a1}  \\
        I_{a2}
    \end{bmatrix}
    +
     \begin{bmatrix}
        K_{e1} & 0 \\
        0 & K_{e2} 
    \end{bmatrix}
     \begin{bmatrix}
        \theta_1 \\
        \theta_2
    \end{bmatrix}
    =
     \begin{bmatrix}
       V_{a1} \\
        V_{a2} 
    \end{bmatrix}
    \end{equation}
    \end{document}
    

Regarding your equations: You wrote theat instead of theta -> changing that should do it:

    $$ B = \frac{J_2}{N_1 N_2}+\frac{m_2 r_2^2}{4 N_1 N_2}+\frac{m_2 r_1 r_2}{2 N_1 N_2} cos(\frac{\theta_{m2}}{N_2}) $$
    $$ C = \frac{-m_2 r_1 r_2}{N_1 N_2}(\frac{\theta_{m1} \theta_{m2}}{N_1}+\frac{\theta_{m2}^2}{2 N_2}) sin\frac{\theta_{m2}}{N_2} $$
    $$ D = J_{m1} +\frac{J_2}{N_2^2}+\frac{m_2 r_2^2}{4 N_2^2} $$
    $$ E = \frac{J_2}{N_1 N_2}+\frac{m_2 r_2^2}{4 N_1 N_2}+\frac{m_2 r_1 r_2}{2 N_1 N_2} cos(\frac{\theta_{m2}}{N_2}) $$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.