2

I have a list of equations and I want them to be centered and aligned to the beginning of the equation and by the equal sign. This is what I tried so far:

\begin{align*}
\mathcal{L}_{a2c} &= \mathbb{E}_{s_t,a_t\sim\pi_{\theta}}[\mathcal{L}_{a2c_{policy}} + \frac{1}{2}\mathcal{L}_{a2c_{value}}]\\
\mathcal{L}_{a2c_{policy}} &= -\log{\pi_{\theta}(a_t|s_t)}(V_t^n-V_\theta(s_t)) - \alpha\mathcal{H}_t^{\pi_\theta}\\
\mathcal{L}_{a2c_{value}} &= {(V_t^n-V_\theta(s_t))}^2 
\end{align*}

but unfortunately, I get:

enter image description here

As the image shows, the equations are aligned by "=" but start in different positions.

Shani Gamrian
  • 167
  • To be honest, I would either align like this or to the left, not keeping the equal signs aligned. – egreg Sep 11 '19 at 17:34

2 Answers2

7

A solution with alignat, and some improvements (in particular, fractional coefficients in medium size look better, in my opinion):

\documentclass[11pt]{book}
\usepackage{mathtools, amssymb, nccmath}

\begin{document}

\begin{alignat*}{2}
 & \mathcal{L}_{a2c} & &= \mathbb{E}_{s_t,a_t\sim\pi_{\theta}}\Bigl[\mathcal{L}_{a2c_\text{policy}} + \mfrac{1}{2}\mathcal{L}_{a2c_\text{value}}\Bigr]\\
 & \mathcal{L}_{a2c_\text{policy}} & &= -\log{\pi_{\theta}(a_t\mid s_t)}\bigl(V_t^n-V_\theta(s_t)\bigr) - \alpha\mathcal{H}_t^{\pi_\theta}\\
 & \mathcal{L}_{a2c_\text{value}} & &= \bigl(V_t^n-V_\theta(s_t)\bigr)^2
\end{alignat*}

\end{document}

enter image description here

Bernard
  • 271,350
3

One option is to place each of the left-hand sides of te equations in equally-sized boxes, and <align> each element to the left. \eqmathbox[LHS][l]{<lhs>}, as defined below, will help with that:

enter image description here

\documentclass{article}

\usepackage{eqparbox,xparse,amsmath,amsfonts}

% https://tex.stackexchange.com/a/34412/5764
\makeatletter
% \eqmathbox[<tag>][<align>]{<math>}
\NewDocumentCommand{\eqmathbox}{o O{c} m}{%
  \IfValueTF{#1}
    {\def\eqmathbox@##1##2{\eqmakebox[#1][#2]{$##1##2$}}}
    {\def\eqmathbox@##1##2{\eqmakebox{$##1##2$}}}
  \mathpalette\eqmathbox@{#3}
}
\makeatother

\begin{document}

\begin{align*}
  \eqmathbox[LHS][l]{\mathcal{L}_{a2c}} &= 
    \mathbb{E}_{s_t, a_t \sim \pi_{\theta}}[\mathcal{L}_{a2c_{\text{policy}}} + \tfrac{1}{2}\mathcal{L}_{a2c_{\text{value}}}] \\
  \eqmathbox[LHS][l]{\mathcal{L}_{a2c_{\text{policy}}}} &= 
    -\log{\pi_{\theta}(a_t|s_t)}(V_t^n - V_\theta(s_t)) - \alpha\mathcal{H}_t^{\pi_\theta} \\
  \eqmathbox[LHS][l]{\mathcal{L}_{a2c_{\text{value}}}} &= {(V_t^n - V_\theta(s_t))}^2 
\end{align*}

\end{document}
Werner
  • 603,163