我不是乳胶方程式方面的专家。我曾在一本书的一章中写过这些方程式，但我忘记了如何在左侧用方程式编号写标签。此外，方程式后面的文本有几行是斜体，我找不到解决方法。哪里出了问题？
（根据建议进行编辑）
\documentclass[a4paper,11pt, twoside, openright]{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[a4paper,top=3.5cm,bottom=3cm,left=3cm,right=3cm]{geometry}
\usepackage{fancyhdr}
\usepackage{setspace}
\usepackage{graphicx}
\usepackage{caption}
\captionsetup{font=small}
\usepackage{topfront}
\usepackage{emptypage}
\usepackage{natbib, authoryear}
\graphicspath{figure}
\usepackage{longtable}
\usepackage{chngcntr}
\usepackage{rotating}
\usepackage{mathtools}
\usepackage{textgreek}
\usepackage{hyperref}
\begin{document}
yi \in Y_{i} \sim mathrm{Multinom}(\pi^1_i , \pi^2_i , \pi^3_i )
\pi^k_i = \frac{exp(\eta^k_i)} {1+ \exp(\eta^2i) + exp(\eta^3i)}\hfill k= 1,...,3
\eta^k_i = ln(\frac{\pi^k_i }{\pi^1_i}) = \beta^k_0 + x_i_1\beta^k_1 + \sum^11_{j_=_3 } x_i_j\beta^k_j \hfill k= 2,3
\eta^1_i = 0
some text which is italic
\end{document}
我还没有解决用 $\pi$ 替换的问题
答案1
在某些情况下，我不得不对其含义进行一些猜测……
\documentclass[a4paper,11pt, twoside, openright]{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\DeclareMathOperator\Multinom{Multinom}
\begin{document}
some text
\begin{equation}
yi \in Y_{i} \sim \Multinom(\pi^1_i , \pi^2_i , \pi^3_i )
\end{equation}
some more text ${x_i}_1$ ?? $\sum^1$ ???
\begin{align}
\pi^k_i &= \frac{\exp(\eta^k_i)} {1+ \exp(\eta^2i) + \exp(\eta^3i)} && k= 1,\dots,3\\
\eta^k_i &= \ln(\frac{\pi^k_i }{\pi^1_i}) = \beta^k_0 + x_{i1}\beta^k_1 + \sum^11_{j=3 } x_{ij}\beta^k_j &&k= 2,3\\
\eta^1_i &= 0
\end{align}
some text which is italic
\end{document}