I've searched this site and found various methods to left-justify math in display style, including adding fleqn to \documentclass, \setlength{\mathindent}{0pt}, and using & within the align environment. But I can't get any of them to work, regardless of which display I environment I use.
I'd like to know how to get every equation in a document to be left-justified, as well as how to get selected equations to be left-justified, hopefully in the simplest way possible. Here's my code:
%&latex
\documentclass[fleqn,9 pt]{article}
\usepackage{diffcoeff}
\usepackage{mathtools}
\usepackage{extsizes}
\usepackage{esdiff, nccmath}
\usepackage{booktabs}
\usepackage[showframe]{geometry}
\usepackage[bottom=.5in,top=1in]{geometry}%ALLOWS ME TO SET MARGINS
\setlength{\voffset}{-0.75in}
\setlength{\parindent}{0pt}
\setlength{\parskip}{15pt}
\setlength{\mathindent}{0pt}
\newcommand{\ffrac}[2]{\ensuremath{\frac{\displaystyle #1}{\displaystyle
#2}}}
\title{\vspace{-25cm}}
\author{}
\date{}
\begin{document}
\section*{Left align minimum working example$}
$$\ln K_P=\sum_{i} \ln\left(\ffrac{p_i^{eq}}{p^o}\right)^{\nu_i}$$
\[
\ln K_P=\sum_{i} \ln\left(\ffrac{p_i^{eq}}{p^o}\right)^{\nu_i}
\]
\begin{align}
& \ln K_P=\sum_{i} \ln\left(\ffrac{p_i^{eq}}{p^o}\right)^{\nu_i}
\end{align}
\begin{gather}
\ln K_P=\sum_{i} \ln\left(\ffrac{p_i^{eq}}{p^o}\right)^{\nu_i}
\end{gather}
\begin{equation}
\ln K_P=\sum_{i} \ln\left(\ffrac{p_i^{eq}}{p^o}\right)^{\nu_i}
\end{equation}
\end{document}
Currently, everything remains centered:

\usepackage{diffcoeff}and\usepackage{esdiff}clash. If I remove the clash, everything is left-aligned except for the$$ ..$$line, but$$should not be used anyway. – Mar 08 '19 at 06:25$$shouldn't be used, but hasn't said why. The reason is thatamsmath(loaded bymathtools) definesfleqnto operate only on display structures defined by basic LaTeX or byamsmath, and$$is a carryover from plain TeX and is not modified for LaTeX. (And that is why it shouldn't be used -- because in cases such as you show here, it won't work.) – barbara beeton Mar 09 '19 at 01:28