Math & Science ⇒ Numbering Theorems

[dward1996]

I am currently working on a final year undergraduate project, and am in the process of writing up my report. I have defined a number of environments

Code: Select all

\documentclass{report}

\newtheorem{theorem}{Theorem}[chapter]
\newtheorem{property}[theorem]{(}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{corollary}[theorem]{Corollary}

\begin{document}

\end{document}

With the above code, the first theorem/proposition etc. in chapter 3 say, is numbered Theorem 3.1. However, in a couple of my chapters I would like to have the theorems numbered by section rather than chapter. I am sure that this can be done using the \renewcommand command, but cannot seem to work out exactly what I need to do. Any help would be greatly appreciated.

[gmedina]

When you say "by section" do you mean including the section counter and removing the chapter counter, or simply the chapter counter followed by the section number and then by the corresponding theorem number?

[dward1996]

When you say "by section" do you mean including the section counter and removing the chapter counter, or simply the chapter counter followed by the section number and then by the corresponding theorem number?

Sorry I hadn't realised how ambiguous I had been. Basically in some chapters, I want to number things as Theorem 3.1.2 say for the second theorem in section 1 of chapter 2.

[gmedina]

All you need to do is to redefine the \thetheorem command (if you want this same behaviour to apply to your properties, definitions, etc. you'll have to redefine \theproperty, \thedefinition, etc.):

Code: Select all

\documentclass{report}
\usepackage{amsthm}

\newtheorem{theorem}{Theorem}[chapter]
\newtheorem{property}[theorem]{(}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{corollary}[theorem]{Corollary}

\begin{document}
\chapter{test chapter one}
\section{test section one one}
\begin{theorem}
a=b
\end{theorem}

% section with theorem counter changed (chapter.section.theorem)
\section{test section one two}
\renewcommand\thetheorem{\thesection.\arabic{theorem}}
\begin{theorem}
a=b
\end{theorem}

% section with theorem counter restored
\section{test section one three}
\renewcommand\thetheorem{\thechapter.\arabic{theorem}}
\begin{theorem}
a=b
\end{theorem}

\end{document}

[dward1996]

Thanks for that gmedina. It works a treat!