Simplest flowchart using TikZ

Question

I would like to have a very simple flowchart using TikZ.

I would very much appreciate if you provide a simple code for this.

For a color, a black and white is fine.

For example, the following is a simple one. But I would like to have blocks of the same width regardless of the text.

\tikzstyle{block} = [draw,rectangle,thick,minimum height=2em,minimum width=2em] \tikzstyle{line} = [draw, very thick, color=black!50, -latex']
\begin{tikzpicture}[node distance = 2cm, auto] 
    \node [block] (init) {initialize model}; 
    \node [block, below of=init] (expert) {expert}; 
    \path [line] (init) -- (expert); 
\end{tikzpicture}

Answer 1

Use tikzset instead of tikzstyle, see here: Should \tikzset or \tikzstyle be used to define TikZ styles?.

Use below=... of instead of below of=, this way you can also set the distance between the nodes.

To have all the blocks with the same size use text width=10em or whatever width you prefer.

If you want to shift the line between the two blocks, you could use xshift=....

If you want a big arrow, change line width=..., and, if you want to shorten it, use shorten >=... for the tip and shorten <=... for the tail.

As cfr told you, don't use arrows but arrows.meta, you can also change the aspect of the arrow tip with [length=..., width=...]. I've choosen Triangle because is similar to the image you posted, but you could choose also Stealth or Latex.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta, positioning}
\tikzset{%
    block/.style = {draw=cyan,rectangle,thick,
        minimum height=2em, text width=10em, align=center},
    line/.style = {draw=cyan, line width=4pt, 
        -{Triangle[length=10pt, width=10pt]}, shorten >=2pt, shorten <=2pt},
}

\begin{document}
\begin{tikzpicture}[node distance = 2cm, auto] 
    \node [block] (init) {initialize model}; 
    \node [block, below=30pt of init] (expert) {expert}; 
    \path [line] (init) -- (expert); 
    \node [block, below=30pt of expert] (third) {third}; 
    \path [line] ([xshift=-1em]expert.south) -- ([xshift=-1em]third.north); 
    \node [block, below=30pt of third] (fourth) {fourth}; 
    \path [line] ([xshift=1em]third.south) -- ([xshift=1em]fourth.north); 
\end{tikzpicture}
\end{document}