为什么符号无法正确呈现？

Question

我有一个包含 3 行方程的方程数组命令。第一行和第二行全部正确，但第三行没有一个符号正确呈现。我使用各种在线 LaTeX 编辑器检查了这个问题，并坚持使用所有这些编辑器。

谁能告诉我出了什么问题？

\begin{eqnarray}
ds^{2}=\frac{\tilde{L}^2}{z^{2}}\left(\left(1-
f(v,z)v'^{2}-2z'v'\right)dx^{2}+dx_2^{2}+dx_3^{2}\right)\\
\sqrt{h}=\frac{\tilde{L}^3}{z^{3}}\left(1-
f(v,z)v'^{2}-2z'v'\right)^{\frac{1}{2}}\qquad , \qquad 
\sqrt{\sigma}=\frac{\tilde{L}^{2}}{z^{2}}\\
\sqrt{h} \cal{R}_{\Sigma}=-\frac{2\tilde{L} Q'z'}{Q^{\frac{3}{2}}z^{2}}-
\frac{6\tilde{L} z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L} z''}
{\sqrt{Q}z^{2}}\\
\sqrt{h}\cal{R}_{\Sigma}=-\frac{2 \tilde{L} Q'z'}{Q^{\frac 32}z^{2}}-
\frac{6\tilde{L}z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L}z''}{\sqrt{Q}z^{2}}
\end{eqnarray}

Answer 1

• 该\cal命令在 LaTeX 2.09 中使用，自 LaTeX2e (1992) 发布以来已过时。它用作字体更改声明，而不是带参数的命令，因此其正确用法是{\cal ...}。相反，它使用\mathcal
• 离题：而是eqnarray使用align或gather（如您使用eqnarray）

\documentclass{article}
\usepackage{amsmath}

\begin{document}
with "garther":
\begin{gather}% changed
ds^{2}=\frac{\tilde{L}^2}{z^{2}}\left(\left(1-
f(v,z)v'^{2}-2z'v'\right)dx^{2}+dx_2^{2}+dx_3^{2}\right)\\
\sqrt{h}=\frac{\tilde{L}^3}{z^{3}}\left(1-
f(v,z)v'^{2}-2z'v'\right)^{\frac{1}{2}}\qquad , \qquad
\sqrt{\sigma}=\frac{\tilde{L}^{2}}{z^{2}}\\
%
\sqrt{h} \mathcal{R}_{\Sigma}
 =-\frac{2 \tilde{L} Q'z'}
        {Q^{\frac{1}{2}} z^{2}} -
\frac{6\tilde{L} z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L} z''}
{\sqrt{Q}z^{2}}\\
%
\sqrt{h}\mathcal{R}_{\Sigma}=-\frac{2}{\tilde{L} Q'z'}{Q^{\frac 32}z^{2}}-
\frac{6\tilde{L}z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L}z''}{\sqrt{Q}z^{2}}
\end{gather}

with "align":
\begin{align}% changed
ds^{2}
    & = \frac{\tilde{L}^2}{z^{2}}
        \left(\left(1 - f(v,z)v'^{2} - 2z'v'\right) dx^{2} + dx_2^{2}+dx_3^{2}\right)        \\
\sqrt{h}
    & = \frac{\tilde{L}^3}{z^{3}}
        \left(1 - f(v,z)v'^{2}-2z'v'\right)^{\frac{1}{2}},
        \qquad
        \sqrt{\sigma}=\frac{\tilde{L}^{2}}{z^{2}}\\
%
\sqrt{h} \mathcal{R}_{\Sigma}% <-- changed
    & = -\frac{2 \tilde{L} Q'z'}{Q^{\frac{1}{2}} z^{2}} -
        \frac{6\tilde{L} z'^{2}}{\sqrt{Q}z^{3}} +
        \frac{4\tilde{L} z''}{\sqrt{Q}z^{2}}\\
%
\sqrt{h}\mathcal{R}_{\Sigma}% <-- changed
    & = -\frac{2}{\tilde{L} Q'z'}{Q^{\frac 32}z^{2}} -
        \frac{6\tilde{L}z'^{2}}{\sqrt{Q}z^{3}} +
        \frac{4\tilde{L}z''}{\sqrt{Q}z^{2}}
\end{align}
\end{document}