Adjust vertical spacing for any combination of text, equations and custom environments

Question

Edit I completely rewrote the question thanks to @pluton's comment.

---

I have a couples of documents which have to fit on two pages. Some of them are short, so nothing needs to be done. But for some others, I need to squeeze vertical spacing.

To do so, I created a variable \mylength which I manually adjust for each document. I would like \mylength to be the spacing above and below any environment, particularly equation and the custom environments defi and theo.

Following @pluton comment, I integrated \addvspace. I still have some problems.

This is the result for \mylength equals to 0pt. It is meant to check the minimal spacing. The output is almost fine, except:

• the vertical space surrounding the equation which, for some reason I don't understand, behaves as if there were text above and below (see above equation (2), above (4), below (5) [I am aware that two equations should not written as so], above (6).

With \mylength equals to 0pt:

---

Now, if I change \mylength from 0pt to 8pt, the result has several problems:

• with no suprise, the space around equation is still wrong
• the spacing between two defi is wrong
• theo is not centered when surrounded by defi (see Theorem 4)

With \mylength equals to 8pt:

Code:

\documentclass[9pt,a4paper]{article}
\usepackage[table]{xcolor}
\usepackage{graphicx}
\usepackage[margin=1.cm,top=1.2cm,bottom=1.3cm,headsep=14pt]{geometry}
\usepackage[utf8]{inputenc}  
\usepackage[T1]{fontenc} 
\usepackage{environ}
\usepackage{tikz}
\usepackage{framed}
\usepackage{amsmath,amsfonts,amssymb}

%%%%%%%%% ENVIRONMENTS %%%%%%%%%%

\newenvironment{mycenter}% to control space after and before environment
  {\addvspace{\mylength}\centering}% \begin{mycenter}[<len>]
  {\par\addvspace{\mylength}}% \end{mycenter}

\NewEnviron{theo}[1]{%

  \begin{mycenter}
\begin{tikzpicture}
  \node[rectangle, rounded corners, inner sep=5pt,minimum width=\textwidth,
    text=black, text opacity=1,
    draw=orange, ultra thick, draw opacity=1,
    fill=orange, fill opacity=.3] 
  (box){%
    \begin{minipage}{.95\textwidth}
      \textbf{#1}\qquad\BODY
  \end{minipage}};
\end{tikzpicture}
\end{mycenter}
}

% for adjustwidth environment
\usepackage[strict]{changepage}

% for definitions
\definecolor{defishade}{rgb}{0.97,0.97,.99}
\newenvironment{defi}{%
\vspace{-1.2mm} % UGLY MANUAL ADJUSTEMENT
\par\addvspace{\mylength}
\setlength{\topsep}{0pt}
  \def\FrameCommand{%
    \hspace{1pt}%
    {\color{black!70}\vrule width 2pt}%
    {\color{defishade}\vrule width 4pt}%
    \colorbox{defishade}%
  }%
  \MakeFramed{\advance\hsize-\width\FrameRestore}%
  \noindent\hspace{-4.55pt}% disable indenting first paragraph
    % \vspace{-8pt}  
  \begin{adjustwidth}{0pt}{7pt}%
  \vspace{1.5pt}\vspace{2pt}%
 \textcolor{black!70}{ \textbf{Definition}\qquad}
}
{%
  \vspace{2pt}
  \end{adjustwidth}\endMakeFramed%
  \vspace{.5mm}
  \addvspace{\mylength}
}




\begin{document}\thispagestyle{empty}
\def\mylength{0pt}
\setlength{\belowdisplayskip}{\mylength} \setlength{\belowdisplayshortskip}{\mylength}
\setlength{\abovedisplayskip}{\mylength} \setlength{\abovedisplayshortskip}{\mylength}


\paragraph{Environment theo}  First, let's check this environment.


\begin{theo}{Theorem} If blah blah blah then
\begin{equation}
1+1=2
\end{equation}
\end{theo}
Everything's fine here.
\begin{theo}{Theorem} If blah blah blah then nothing.
\end{theo}%
\begin{theo}{Theorem} If blah blah blah then nothing.
\end{theo}%
Everything's fine here.
\begin{theo}{Theorem} If blah blah blah then nothing.
\end{theo}%
\begin{equation}1-1=0\end{equation}
\textcolor{red}{\bf Why is the distance between the above equation and the theorem so large?}

\paragraph{Environment defi}  Now, let's check this second environment. 
\begin{defi}Below, it's OK for \verb?0pt? and \textcolor{red}{too large} for \verb?8pt?.\end{defi}
\begin{defi}Nothing special.\end{defi}
Spacing is OK for 0pt but not centered (vertically) as between the two first theorems for 10pt.\begin{defi}Here, it's OK.\end{defi}
\begin{theo}{Theorem 2} If blah blah blah then
\begin{equation}
1+1=2
\end{equation}
\end{theo}
\begin{equation}
2+3=5 \text{ when two environments are following eachother, the vertical spacing adds up.}  
\end{equation}
\begin{equation}
1+1=2
\end{equation}%
%qsdfqsdf
\begin{defi}\textcolor{red}{\bf Why is the distance between the above equation and the present, and previous definitions, so large?}
\end{defi}
\begin{theo}{Theorem 4} \textcolor{red}{Theorem is not centered between two definitions for 8pt.}
\end{theo}%
\begin{defi}\textcolor{red}{Space too large below for 10pt.}\end{defi}
\begin{equation}
1+1=2%
\end{equation}%
%sdfqssddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
\begin{defi}Kombucha is a bloh bloh bloh.\end{defi}
\end{document}

Answer 1

• Redefining the environment mycenter which was causing some trouble, with:

  \newenvironment{mycenter}%
  {\parskip=0pt\par\addvspace{\mylength}\centering}%
  {\par\addvspace{\mylength}\noindent\ignorespacesafterend}%
  

• Redefining the custom environment defi using tikz as for the theo environment, so that I could understand what the code,

• Changing \mylength to an extendable length as suggested by Sigur and elford with \mylength{8pt plus 4pt minus 6pt},
• And using \addvspace to avoid adding a vertical space twice,

I was able to produce this, which fit my needs:

Complete code:

\documentclass[9pt,a4paper]{article}
\usepackage[table]{xcolor}
\usepackage{graphicx}
\usepackage[margin=1.cm,top=1.2cm,bottom=1.3cm,headsep=14pt]{geometry}
\usepackage[utf8]{inputenc}  
\usepackage[T1]{fontenc} 
\usepackage{environ}
\usepackage{tikz}
\usepackage{framed}
\usepackage{amsmath,amsfonts,amssymb}

%%%%%%%%% ENVIRONMENTS %%%%%%%%%%

\newenvironment{mycenter}% to control space after and before environment
  {\parskip=0pt\par\addvspace{\mylength}\centering  }% \begin{mycenter}[<len>]
  {\par\addvspace{\mylength}\noindent\ignorespacesafterend}% \end{mycenter}

\NewEnviron{theo}[1]{%

  \begin{mycenter}
\begin{tikzpicture}
  \node[rectangle, rounded corners, inner sep=5pt,minimum width=\textwidth,
    text=black, text opacity=1,
    draw=orange, ultra thick, draw opacity=1,
    fill=orange, fill opacity=.3] 
  (box){%
    \begin{minipage}{.95\textwidth}
      \textbf{#1}\qquad\BODY
  \end{minipage}};
\end{tikzpicture}
\end{mycenter}
}

\definecolor{defishade}{rgb}{0.97,0.97,.99}
\NewEnviron{defi}{%
  \begin{mycenter}
\begin{tikzpicture}
  \node[rectangle, inner sep=5pt,minimum width=\textwidth,
    text=black, text opacity=1,
    draw=none, ultra thick, draw opacity=1,
    fill=defishade, fill opacity=1,
    line width=0pt,
    append after command={
      (\tikzlastnode.north west) edge [line width=.8mm,color=black!70]
(\tikzlastnode.south west)}] 
  (box){%
    \begin{minipage}{.95\textwidth}
      \textcolor{black!70}{\textbf{Définition}}\qquad\BODY
  \end{minipage}};
\end{tikzpicture}
\end{mycenter}
}


\begin{document}\thispagestyle{empty}
\def\mylength{8pt plus 4pt minus 6pt}
\setlength{\belowdisplayskip}{\mylength} \setlength{\belowdisplayshortskip}{\mylength}
\setlength{\abovedisplayskip}{\mylength} \setlength{\abovedisplayshortskip}{\mylength}


First, let's check this environment.


\begin{theo}{Theorem} If blah blah blah then
\begin{equation}
1+1=2
\end{equation}
\end{theo}
Everything's fine here.
\begin{theo}{Theorem} If blah blah blah then nothing.
\end{theo}%
\begin{theo}{Theorem} If blah blah blah then nothing.
\end{theo}%
Everything's fine here.
\begin{theo}{Theorem} If blah blah blah then nothing.
\end{theo}%
\begin{equation}1-1=0\end{equation}
text text text


 Now, let's check this second environment. 
\begin{defi}A fool is a pool with an \textit{f}.\end{defi}
\begin{defi}Nothing special.\end{defi}
I can write whatever I want, who cares.
\begin{defi}You need to learn all definitions.\end{defi}
\begin{theo}{Theorem 2} If blah blah blah then
\begin{equation}
1+1=2
\end{equation}
\end{theo}
\begin{equation}
\cos \pi=-1
\end{equation}
\begin{equation}
1+1=2
\end{equation}%
\begin{defi} \LaTeX\  is your friend.
\end{defi}
\begin{theo}{Theorem 4} Let's all love each other.
\end{theo}%
\begin{defi}Someone nasty is not nice.\end{defi}
\begin{equation}
1+1=2%
\end{equation}%
\begin{defi}Kombucha is a bloh bloh bloh.\end{defi}
\end{document}