Why ```tikzpicture``` appears on a separated page?

Question

I am beginner in tikz environment, so I am really sorry if this question seems quite naive. I had a flow chart drawn using tikzpicture, as you see its not that complicated. The problem is I want the flow chart do be directly after the last text, not on a separated page! It appears on a separated page anyway, regardless of its size! Any one could kindly help?

This is my code...

\documentclass[English,MSC,Times,NoIndent,IEEE]{mfthesis}
\usepackage{layout}
\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric,arrows}
\usepackage{ragged2e}
\usepackage{times}
\usepackage{float}
\usepackage{amsmath}
\usepackage{mathtools}

\begin{document}

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\tikzstyle{rect} = [draw, rectangle, fill=gray!10, text width=6em, text centered, minimum height=2em]
\tikzstyle{elli} = [draw, ellipse, fill=white!20, node distance=3cm, minimum height=2em]
\tikzstyle{circ} = [draw, circle, fill=white!20, node distance=3cm, minimum width=8pt, inner sep=10pt]
\tikzstyle{diam} = [draw, diamond, fill=gray!20, text width=6em, text badly centered, outer sep=0, inner sep=0pt]
\tikzstyle{line} = [draw, -latex']
\begin{figure}
\begin{center}
    \begin{tikzpicture}
        % Place nodes
        \node [rect, rounded corners=10pt, line width=0.5mm, node distance = 2cm] (step1) {start};
        \node [rect, below of=step1, line width=0.5mm, node distance = 2cm] (step2) {Measure $i_{dq}(k),\theta(k)$};
        \node [rect, below of=step2, line width=0.5mm, node distance = 2cm] (step3) {n$=$0};
        \node [rect, below of=step3, line width=0.5mm, node distance = 2cm] (step4) {n$=$n$+$1};
        \node [rect, below of=step4, text width=10em, minimum height=3em, line width=0.5mm, node distance = 2cm] (step5) {Calculate $i_{dq}^p(k+1)$ from Eqns 3.13, 3.14};
        \node [rect, below of=step5, text width=14em, line width=0.5mm, node distance = 2cm](step6) {Calculate cost function\\ $g=(i_d^*-i_d^p(k+1))^2+(i_q^*-i_q^p(k+1))^2$};
        \node [diam, below of=step6, line width=0.5mm, node distance=3cm] (step7) {n$>$7};
        \node [rect, below of=step7, text width=10em, line width=0.5mm, node distance=3cm] (step8) {Apply switching state};
        \node [rect, minimum height=3em, left of=step5, line width=0.5mm, node distance=5cm] (step9) {Next sampling period};
        % Draw edges
        \path [line, line width=0.75mm] (step1) -- (step2);
        \path [line, line width=0.75mm] (step2) -- (step3);
        \path [line, line width=0.75mm] (step2) -- (step3);
        \path [line, line width=0.75mm] (step3) -- (step4);
        \path [line, line width=0.75mm] (step4) -- (step5);
        \path [line, line width=0.75mm] (step5) -- (step6);
        \path [line, line width=0.75mm] (step6) -- (step7);
        \path [line, line width=0.75mm] (step7) -- node [right,near start]{True}(step8);
        \path [line, rounded corners, line width=0.75mm] (step7) --++ (4,0) node [above,near start]{False}|-(step4);
        \path [line, rounded corners, line width=0.75mm] (step8) -| (step9);
        \path [line, rounded corners, line width=0.75mm] (step9) |- (step2);
    \end{tikzpicture}
    \caption{Flow diagram of motor current control using FS-MPC}
    \label{Fig.4.9}
\end{center}
\end{figure}

\end{document}

Answer 1

It's because you've put the tikzpicture inside a figure environment. Figure environments are floats, which means that LaTeX will move them to the next page if it thinks that doing so gives the best page layout.

There are options you can use to influence what LaTeX does with floats - see

https://www.overleaf.com/learn/latex/Positioning_of_Figures

for good information on this. Or you could just not use the figure environment, and use an alternative to \caption for the title of your tikzpicture.

Answer 2

You have two problems:

• you not use figure placement option, I suggest you to use htbp (see wiki/LaTeX/Floats,Figures and Captions)
• your figure is huge and occupancy more space as is (default) reserved for floats on each page. This you can solve on two ways:
  • reduce image size, for example as shown in MWE below (it use consistent smaller distance between nodes)
  • change default settings for amount of text on page (see Controling LaTeX floats)

\documentclass{article}%[English,MSC,Times,NoIndent,IEEE]{mfthesis}
\usepackage{layout}
\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,
                chains,
                positioning,
                shapes.geometric}
\usepackage{ragged2e}
\usepackage{times}
\usepackage{float}
%\usepackage{amsmath}
\usepackage{mathtools}% it load amsmath

%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%

\begin{document}

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   \begin{figure}[htbp]
\centering
    \begin{tikzpicture}[
node distance = 8mm and 12mm,
  start chain = going below,
  base/.style = {draw, thick, fill=gray!10, align=center, 
                 inner xsep=3mm, inner ysep=2mm},
  rect/.style = {base},
  elli/.style = {ellipse, base},
  circ/.style = {circle, fill=graye!10, minimum size=12pt},
  diam/.style = {diamond, base, aspect=1.5},
  line/.style = {draw, rounded corners, -Stealth, semithick},
                    ]
% Place nodes
    \begin{scope}[nodes = {on chain, join=by line}]
\node [rect, rounded corners=10pt] (step1) {start};
\node [rect] (step2) {Measure\\ 
                      $i_{dq}(k),\theta(k)$};
\node [rect] (step3) {n$=$0};
\node [rect] (step4) {n$=$n$+$1};
\node [rect] (step5) {Calculate $i_{dq}^p(k+1)$\\
                      from Eqns 3.13, 3.14};
\node [rect] (step6) {Calculate cost function\\
                      $\begin{multlined}
                      g = (i_d^*-i_d^p(k+1))^2 \\
                            +(i_q^*-i_q^p(k+1))^2
                      \end{multlined}$};
\node [diam] (step7) {n$>$7};
\node [rect] (step8) {Apply switching state};
    \end{scope}
\node [rect, left=of step5] (step9) {Next sampling period};
% Draw edges
\path[line] (step8) -| (step9);
\path[line] (step9) |- (step2);
%
\path       (step7) -- node [right,near start]{True}    (step8);
\draw[line] (step7) --++ (3,0) node [above,near start]{False} |-(step4);
    \end{tikzpicture}
\caption{Flow diagram of motor current control using FS-MPC}
\label{Fig.4.9}
    \end{figure}
\end{document}

Note:

• use of tikzstyle is deprecated. Instead it use tikzset or enclose styles settings in tikzpicutere options as it is done in above MWE
• to have equal distance between nodes, use positioning library and its syntax, for example below=of <coordinate name>
• image code can be noticable shortened by use of the chains library and its macro join=by <style name>