尝试在下标中使用两个 \betas 时出现错误消息

Question

我正在尝试使用

$\simga_{\beta_1 \beta_2}$ and $\simga_{\beta_2 \beta_1}$

在我的文本中。但是，我总是收到以下错误消息，我不明白

! Undefined control sequence.
l.266 ...ma_{\beta_1}^2,\sigma_{\beta_2}^2, \simga
_{\beta_1\beta_2}$ and $\s...
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

我该如何解决这个问题？

Answer 1

您有\simga而不是\sigma。

一般规则：在出现错误的行的顶部末尾有一个错误原因。在这种情况下\simga。