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What I'm doing:

\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{eucal}
\usepackage{amssymb}
\usepackage{mathrsfs}

% don't know what some of those do, but i think all the math related ones are
% there
% there are more packages being imported though

Then I try:

\textbf{w_{n+1}} = \textbf{w_{n}} + e\eta\textbf{x}(n) \\
\textbf{\Delta}\textbf{w} = e\eta\textbf{x}

% above doesn't work, complains about missing $

\textbf{$w_{n+1}$} = \textbf{$w_{n}$} + e\eta\textbf{$x$}(n) \\
\textbf{$\Delta$}\textbf{$w$} = e\eta\textbf{$x$}

% above compiles, but no bold and no newline
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4 Answers 4

up vote 8 down vote accepted

You could bold an equation with \boldsymbol. Use \align for multiline equation with alignment.

\begin{align}
\boldsymbol{w_{n+1}} &= \boldsymbol{w_n} + e\eta\boldsymbol{x}(n) \\
\boldsymbol{\Delta w} &= e\eta\boldsymbol{x}
\end{align}
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Tried both \boldsymbol and \boldmath and neither worked. Without the $ it compiles, but then the text isn't bold. And with the $ it doesn't compile. –  bada Aug 8 '10 at 7:10
    
@bada: Try to \usepackage{amsbsy} — although amsmath already loaded it. –  KennyTM Aug 8 '10 at 7:21
    
I added a \begin{split} after the \begin{align} and an \end{split} before the \end{align} and it worked the way I wanted. –  bada Aug 8 '10 at 7:32
1  
try \(\mathbf{A}\) inside math environment or \boldmath\(A\) before it –  Crowley Aug 9 '10 at 7:19

\textbf is for text mode, not math mode. Also, inline math ($ ... $) is for use inline, and so does not produce new lines. This is pretty basic math stuff for TeX: perhaps you should read something like Math Mode by Herbert Voss (type texdoc mathmode at the Terminal/Command Line).

I think you would be best using the align environment:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
  \mathbf{w_{n+1}}  &= \mathbf{w_{n}} + e\eta\mathbf{x}(n) \\
  \mathbf{\Delta w} &= e\eta\mathbf{x}
\end{align}
\end{document}
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I'm getting a black square instead of \Delta when I use that. With \delta it's fine though. Do you know how I could fix it? Also, this gives the second line an equation number of its own, which isn't what I need. ;/ –  bada Aug 8 '10 at 7:18
    
\usepackage{bm} \bmdefine\bDelta{\Delta} And then use \bDelta to get a bold \Delta –  Martin Heller Aug 8 '10 at 11:40

Use $\mathbf{w_{n+1}}$. However, if you want bold symbols, you'd have to use $\pmb{\eta}$

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It is unfortunate that the comment of Crowley here above is not more highlighted. He give me the answer I search : using \boldmath before the eqn environment, all the math portion is in bold font and the text stay normal.

An example of my code:

   \boldmath\begin{align*}
    p(X,Y) \Leftrightarrow
                & minimal(X) \\
                & \qquad \wedge directly-solve(X,Y) &&\mbox{ (cas de base)}\\
                & \vee \\
                & \neg minimal(X) \\
                & \qquad \wedge decompose(X,partX,restX) &&\mbox{ (diviser)}\\
                & \qquad \wedge process(partX,part-Y) &&\mbox{ (traitement interne)}\\
                & \qquad \wedge p(restX,restY) &&\mbox{ (appel récursif)}\\
                & \qquad \wedge compose(partY,restY,Y) &&\mbox{ (recomposer)}\\
    \end{align*}

Thanks

resultat

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