How to left align equation numbering within multicolum?

Question

I have the following code:

\documentclass[11pt, spanish]{article}
%\usepackage{babel}
\usepackage[latin1]{inputenc}
\usepackage{geometry}
\geometry{legalpaper, 
a4paper,
%top=25mm, 
%bottom=25mm, 
left=30mm,
right=30mm}

\usepackage{multicol}

\usepackage{hyperref}


\usepackage[fleqn]{mathtools}
%\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{relsize}
\usepackage{mathrsfs}
\numberwithin{equation}{section}
%\setlength{\jot}{1.5ex}%10pt}
\renewcommand{\theequation}{IV.\thesection.\arabic{equation}}

\title{Control discreto}

\begin{document}

\section{Asignación de especificaciones}\label{SPECS}
\vspace{-12mm}
\begin{multicols}{2}
\begin{equation}
G_{1}(s) = \dfrac{k_{c}} {\tau_{c} * s + 1} \label{REF1}
\end{equation}
\begin{equation}
G_{2}(s) = \dfrac{\omega_{n}^2} {s^2 + 2*\zeta*\omega_{n}*s + \omega_{n}^2} \label{REF2}
\end{equation}
\end{multicols}

\end{document}

This produces the following output:

Is almost OK, but:

• I'd like equation numbering to have same spacing for both equations (doesn't matter automatic spacing o specifying it)
• I'd like to know if there is another approach to get rid of the blank space before the multicolumns without \vspace{-12mm}, maybe something more 'rigorous'?.

On the other hand, i dont really understand why not including hyperref package produces this output:

Hope anyone find this question easy to answer and help me, is the final touch i need for my thesis.
Thanks in advance.

Answer 1

First, your two questions don't fit the title, so I'm answering all three.

1. Title: How to left align the question numbers: simply add the option leqno to \documentclass[…]{article}

2. Same spacing for both equations: This happens automatically then.

3. No vertical space above the multicolumn: Just as Skillmon pointed out in his comment: add \setlength{\multicolsep}{0pt} before the multicolumn.

So, the corrected code would be:

\documentclass[leqno,11pt, spanish]{article}
%\usepackage{babel}
\usepackage[latin1]{inputenc}
\usepackage{geometry}
\geometry{legalpaper, 
a4paper,
%top=25mm, 
%bottom=25mm, 
left=30mm,
right=30mm}

\usepackage{multicol}

\usepackage{hyperref}


\usepackage[fleqn]{mathtools}
%\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{relsize}
\usepackage{mathrsfs}
\numberwithin{equation}{section}
%\setlength{\jot}{1.5ex}%10pt}
\renewcommand{\theequation}{IV.\thesection.\arabic{equation}}

\title{Control discreto}
\setlength{\multicolsep}{0pt}
\begin{document}

\section{Asignación de especificaciones}\label{SPECS}
\vspace{-12mm}
\begin{multicols}{2}
\begin{equation}
G_{1}(s) = \dfrac{k_{c}} {\tau_{c} * s + 1} \label{REF1}
\end{equation}
\begin{equation}
G_{2}(s) = \dfrac{\omega_{n}^2} {s^2 + 2*\zeta*\omega_{n}*s + \omega_{n}^2} \label{REF2}
\end{equation}
\end{multicols}

\end{document}

Output:

Answer 2

This reserves to each equation a space proportional to its width.

\documentclass[11pt, spanish]{book}
\usepackage{babel}
%\usepackage[latin1]{inputenc}
\usepackage{geometry}
\geometry{
  a4paper,
  %top=25mm, 
  %bottom=25mm, 
  left=30mm,
  right=30mm,
}

\usepackage[fleqn,leqno]{mathtools}
\usepackage{amsfonts}
\usepackage{environ,xparse}

\usepackage{lipsum} % for context

\usepackage{hyperref}

\renewcommand{\thechapter}{\Roman{chapter}}

\numberwithin{equation}{section}

\ExplSyntaxOn
\NewEnviron{doubleequation}
 {
  \saiz_doubleeq:V \BODY
 }

\seq_new:N \l__saiz_doubleeq_seq
\box_new:N \l__saiz_doubleeq_box
\fp_new:N \l__saiz_doubleeq_l_fp
\fp_new:N \l__saiz_doubleeq_r_fp

\cs_new_protected:Nn \saiz_doubleeq:n
 {
  \seq_set_split:Nnn \l__saiz_doubleeq_seq { \\ } { #1 }
  % measure the left equation
  \hbox_set:Nn \l__saiz_doubleeq_box
   {
    \cs_set_eq:NN \label \use_none:n
    $\displaystyle\seq_item:Nn \l__saiz_doubleeq_seq { 1 }$
   }
  \fp_set:Nn \l__saiz_doubleeq_l_fp
   { \dim_to_fp:n { \box_wd:N \l__saiz_doubleeq_box } }
  % measure the right equation
  \hbox_set:Nn \l__saiz_doubleeq_box
   {
    \cs_set_eq:NN \label \use_none:n
    $\displaystyle\seq_item:Nn \l__saiz_doubleeq_seq { 2 }$
   }
  \fp_set:Nn \l__saiz_doubleeq_r_fp
   { \dim_to_fp:n { \box_wd:N \l__saiz_doubleeq_box } }
  %
  \[
  \setlength{\abovedisplayskip}{0pt}
  \begin{minipage}
   {
    \fp_eval:n
     {
      \l__saiz_doubleeq_l_fp / ( \l__saiz_doubleeq_l_fp + \l__saiz_doubleeq_r_fp )
     }
    \displaywidth
   }
   \begin{equation}\seq_item:Nn \l__saiz_doubleeq_seq { 1 }\end{equation}
  \end{minipage}
  \begin{minipage}
   {
    \fp_eval:n
     {
      \l__saiz_doubleeq_r_fp / ( \l__saiz_doubleeq_l_fp + \l__saiz_doubleeq_r_fp )
     }
    \displaywidth
   }
   \begin{equation}\seq_item:Nn \l__saiz_doubleeq_seq { 2 }\end{equation}
  \end{minipage}
  \]
 }
\cs_generate_variant:Nn \saiz_doubleeq:n { V }
\ExplSyntaxOff

\begin{document}

\setcounter{chapter}{3}

\chapter{Control discreto}

\section{Asignación de especificaciones}\label{SPECS}

\lipsum*[3]
\begin{doubleequation}
G_{1}(s) = \frac{k_{c}} {\tau_{c}s + 1} \label{REF1}
\\
G_{2}(s) = \frac{\omega_{n}^2} {s^2 + 2\zeta\omega_{n}s + \omega_{n}^2} \label{REF2}
\end{doubleequation}
\lipsum*[4]
\begin{equation}
G_{3}(s)=s^2
\end{equation}
\lipsum[5]

\end{document}

Answer 3

As Dave sugest, minipage is the proper option for this case:

\begin{minipage}{0.4\linewidth}
\begin{equation}
G_{1}(s) = \dfrac{k_{c}} {\tau_{c} * s + 1} \label{REF1}
\end{equation}
\end{minipage}
\begin{minipage}{0.55\linewidth}
\begin{equation}
G_{2}(s) = \dfrac{\omega_{n}^2} {s^2 + 2*\zeta*\omega_{n}*s + \omega_{n}^2} \label{REF2}
\end{equation}
\end{minipage}

As you can see, the spacing between each equation and its numbering is almost the same. What i wanted to avoid was having the multicolumn space badly distributed (as shown in the first example i posted).

The problem was quite simple actually, multicolumn environment splits the linewidth in two, making second equation be almost overlapped with it's numbering.
To solve this the easier way i found is to manually adjust the "column" width, not really a rigorous way but worked for me (as i only have few of this cases).

On the other hand, \setlength\multicolsep{0pt} trick does the job when using multicolumn enviroment.

Thanks everyone for your help