I want to tag my equations with parallel aligned environments. The code is shown below

& \bold{H}_1^\top\bold{x}_1^*+\bold{K}_1^\top\bold{y}+\bold{U}(\omega_t)= \bold{r}_1:\\
& \bold{A}_3^\top\bold{y}\leq \bold{b}_3:
& \boldsymbol{\gamma}_1(\omega_t), \\
& \boldsymbol{\zeta}_1(\omega_t), 

The output should be two aligned equations, and my goal is to tag them using \tag.

I have tried to add \tag to the first \begin{aligned} block and the second block, but they all failed with an error saying

Package amsmath Error: \tag not allowed here

I have searched the forum but there is none regarding to the tag for double aligned equation. I need to use \begin{equation*} instead of \begin{equation} to allow \tag, since I want to make my own tags.

Thank you in advance!


  • 1
    it's probably easier to just use 2 minipages similar to Two columns of equations, aligned and just one number per column
    – Troy
    Nov 30 '18 at 0:25
  • \tag only works in math environment which is normally numbered. like equation, align etc and not in equation*
    – Zarko
    Nov 30 '18 at 0:35
  • Package mathtools has the \newtagform and \usetagform commands if you want to customise tags.
    – Bernard
    Nov 30 '18 at 0:56
  • Simply use align and array environment.
    – user156344
    Nov 30 '18 at 6:44

Maybe it is something like this you're after?

\documentclass[10pt, a5paper]{book}
\usepackage{mathtools, amssymb}



\noindent\begin{tabularx}{\linewidth}{@{}>{\hsize=1.2\hsize \compress\arraybackslash}X @{\qquad} >{\hsize=0.8\hsize\compress\arraybackslash}X@{}}
{ \begin{subequations}\begin{align}
& \mathbf{H}_1^\top\mathbf{x}_1^*+\mathbf{K}_1^\top\mathbf{y}+\mathbf{U}(\omega_t)= \mathbf{r}_1:\\
& \mathbf{A}_3^\top\mathbf{y}\leq \mathbf{b}_3:
{ \begin{subequations}\begin{align}
& \boldsymbol{\gamma}_1(\omega_t), \\
& \boldsymbol{\zeta}_1(\omega_t),


enter image description here

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