fig1

fig1.tex

\documentclass[tikz]{standalone}

\usepackage{tikz}
\usetikzlibrary{math}

\begin{document}
    \begin{tikzpicture}
        \tikzmath { \total = 6; }
        \draw [help lines] (0,0) grid (\total, \total);
        \foreach \row  in {1,2,...,\total}
        \foreach \x in {1,...,\row} {
            \filldraw (\x,\row) circle [radius=0.25];
        }
\end{tikzpicture}
\end{document}