\documentclass[a4paper,12pt]{report}
\usepackage{amsmath}
\usepackage{systeme}
\usepackage{amssymb}
\usepackage{subfiles} 
\usepackage[english]{babel}
\usepackage[dvipsnames]{xcolor}
\usepackage{graphicx}
\usepackage{xcolor}
\usepackage{sectsty}
\usepackage{framed}
\usepackage{titlesec}
\usepackage[T1]{fontenc}
%Options: Sonny, Lenny, Glenn, Conny, Rejne, Bjarne, Bjornstrup
%\usepackage[Glenn]{fncychap}

\graphicspath{ {./img/} }
\definecolor{mypink}{cmyk}{0, 0.7808, 0.4429, 0.1412}
\definecolor{mygray}{gray}{0.6}
\definecolor{DarkGreen}{RGB}{0,100,0}
\definecolor{GoodGreen}{RGB}{46,139,87}

\newcommand\barra[1]{\mathbb{#1}}
\newcommand\hnn{h_{NN}}
\newcommand\hknn{h_{k-NN}}
\newcommand\knn{K_{NN}}
\newcommand\nl{N_{\ell}}
\newcommand\sll{S_{\ell}}
\newcommand\red[1]{\textcolor{BrickRed}{#1}}
\newcommand\bred[1]{\textcolor{Red}{\textbf{#1}}}
\newcommand\blue[1]{\textcolor{Blue}{\textbf{#1}}}
\newcommand\gray[1]{\textcolor{mygray}{#1}}
\newcommand\col[2]{\textcolor{#2}{#1}}
\newcommand\expt[1]{$\barra{E}\left[ \,{#1}\, \right] $}

%\titleformat{\chapter}[display]
%  {\normalfont\bfseries}{}{0pt}{\Large}
\titleformat{\chapter}[display]
  {\normalfont\bfseries}{}{0pt}{\Huge\color{Blue}}
\titlespacing*{\chapter}{0pt}{-80pt}{40pt}
\chapterfont{\color{Blue}}
\sectionfont{\color{DarkGreen}}
\subsectionfont{\color{red}}


  
\begin{document}

\begin{titlepage}
    \begin{center}
        \vspace*{0.1cm}
            
        \Huge
        \textbf{\col{Statistical Methods for \\ Machine Learning}{Blue}}        \vspace{0.5cm}

 \includegraphics[width=.5\linewidth]{unimi}
            
        \vspace{0.5cm}
        \LARGE
        Data Science and Economics \\
                    Università degli Studi di Milano\\
                            \vspace{0.5cm}


        \vspace{1.5cm}
            
        \textbf{Andrea Ierardi}
            
        \vfill
            
        Lecture notes
            
        \vspace{1cm}
            
 \includegraphics[width=0.9\linewidth]{front}
                        
    \end{center}
\end{titlepage}


\newpage
\tableofcontents
%\listoftables
\listoffigures

\newpage

\subfile{lectures/lecture1}


\newpage
\subfile{lectures/lecture2}

\newpage
\subfile{lectures/lecture3}

\newpage
\subfile{lectures/lecture4}


\newpage
\subfile{lectures/lecture5}


\newpage
\subfile{lectures/lecture6}


\newpage
\subfile{lectures/lecture7}


\newpage
\subfile{lectures/lecture8}


\newpage
\subfile{lectures/lecture9}


\newpage
\subfile{lectures/lecture10}

\newpage
\subfile{lectures/lecture11}

\newpage
\subfile{lectures/lecture12}

\newpage
\subfile{lectures/lecture13}

\newpage
\subfile{lectures/lecture14}
\newpage
\subfile{lectures/lecture15}
\newpage
\subfile{lectures/lecture16}

\newpage
\subfile{lectures/lecture17}

\newpage
\subfile{lectures/lecture18}

\newpage
\subfile{lectures/lecture19}

\newpage
\subfile{lectures/lecture20}
\newpage

\newpage
\subfile{lectures/lecture21}
\newpage
\bibliographystyle{abbrv}
\bibliography{main}

\end{document}
%This is never printed