Title page not showing up in subfile{} when included in main.tex

Question

I am compiling a different documents of article class type and I am using a main tex file of report class to compile it into one pdf file. I used subfile{} to do so but the \maketitle{} page in documents are not showing up. How can I make it so without complicating anything? My main tex file say Lab_Report.tex looks like

\documentclass[12pt]{report} %article also works
\usepackage{subfiles}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{float}
\usepackage{parskip}
\usepackage{siunitx}
\title{}
\begin{document}
\maketitle 
\subfile{report1}
\subfile{report2}
\end{document}

my report.tex looks like

\documentclass{article}
\usepackage{amsmath} 
%assume all necessary packages included
\title{Report 1 - Make something}
\date{1st April 2022}
\begin{document}
\maketitle
\newpage
\subsection{Aim:}
To do something
\subsection{Apparatus:}
Whatever you have now
\end{document}

The end result is that all included files are present but without the \maketitle page. I am quite new to Latex so my code might seem silly.

Answer 1

The subfiles package is not meant to be used the way you were trying to use it. The included files are meant to be parts of the main document, not separate documents with a different document class. In fact, I'm surprised you didn't just get errors when you tried to use it with the subfiles having the "article" document class. All subfiles are supposed to use the "subfiles" document class.

See its documentation, which reads:

The subfiles have to start with the line:

\documentclass[main file name]{subfiles}

which loads the class subfiles. Its only ‘option’, which is actually mandatory, gives the name of the main file. This name follows TEX conventions: .tex is the default extension, the path has to be provided if the main file is in a different directory, and directories in the path have to be separated by / (not ). Thus, we have the following structure.

If LATEX is run on the subfile, the line \documentclass[..]{subfiles} is replaced by the preamble of the main file (including its \documentclass command). The rest of the subfile is processed normally.

As you can see, the subfiles are not supposed to have their own preambles. The package replaces their preambles with the preamble of the main document. Their own preambles are ignored. So the \title and \date commands in your example preambles are just being ignored when the main file is compiled.

Moreover, a single document doesn't usually have multiple \maketitle commands in it. If you need to have multiple \maketitle commands, you would need to load the titling package.

As I see it, you have three options.

Option A

This is closest to what you were trying. Load the titling package in the main file, to allow for multiple \maketitle commands.

\documentclass[12pt]{report}
\usepackage{subfiles}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{float}
\usepackage{parskip}
\usepackage{siunitx}
\usepackage{titling}
\title{Main title}
\author{Author}
\date{Main date}
\begin{document}
\maketitle
\subfile{report1}
\subfile{report2}
\end{document

Move the \title and \date commands in the subfiles to after \begin{document} so they are actually registered (remember the premable is ignored). You can remove any \usepackage commands; they are ignored too. Just make sure the packages you needed are loaded in the main file.

\documentclass[main]{subfiles}
\begin{document}
\title{Report 1 - Make something}
\date{1st April 2022}
\maketitle
\subsection*{Aim:}
To do something
\subsection*{Apparatus:}
Whatever you have now
\end{document}

Of course, the article class is not used at all here, so the titles will be in the style of report (that is, they will be title pages rather than just a heading) by default. The titling package however does let you change the style of the titles. See its documentation.

Option B

Treat the subfiles as "chapters" of the report, since the report class supports chapters, and indeed, expects them. (Your \subsections are not numbered, but if they were, you would notice the numbering starts with 0.0 for the chapter/section as no chapter or section commands were given.) This option actually makes more sense to me, since it uses the report class more the way it was intended.

The subfiles would then be simpler:

\documentclass[main]{subfiles}
\begin{document}
\chapter*{Report 1 - Make something} % remove the * if you want it numbered
\subsection*{Aim:}
To do something
\subsection*{Apparatus:}
Whatever you have now
\end{document}

Then instead of new \maketitle commands, you could just use the chapter heading. If you need to style the chapter headings, or put them on their own pages, something like the titlesec package would allow for that (including adding a date if you needed that).

Option C

You can do what you did. Prepare many separate article class documents, and combine with a main file that uses the pdfpages package, or use a similar tool. This option makes more sense to me if your separate documents really are separate "articles" and not chapters of a single work, and you just need them in a single PDF for some reason