# What font does \mathbf use?

I'd like to format some mathematics text with vectors using fonts consistent with the LaTeX conventions I've been using over the years. I know how to bold the text, but that doesn't change the output too much and I suspect I also have to change the font for consistency.

What font does \mathbf{x} use?

EDIT: for reference, the packages I am using are:

\usepackage{color}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{graphicx}
\usepackage{subfigure}
\usepackage{titlesec}
\usepackage{indentfirst}


but the AMS packages are probably the ones that are relevant.

-
Depends on your math font setup. –  Ulrike Fischer Feb 24 '12 at 16:09
I believe your question can't be answered precisely without quite a bit more information about the font family you use. For instance, if you use pdf(la)tex as the engine, if the font family in use is Computer Modern, and if the standard font size of the document is 10pt, (La)TeX uses one or more of cmbx10, cmbx8, cmbx7, cmbx6, and cmbx5 when it encounters the \mathbf command; the exact font size depends on whether the entity in question is set in textstyle, scriptstyle, or scriptscriptstyle. –  Mico Feb 24 '12 at 16:17
None of the packages alter math fonts so you get the default as mentioned in my and other answers: Computer Modern bold extended –  Frank Mittelbach Feb 24 '12 at 16:52

There isn't a definite answer to a question like this as it depends on what packages you load. But straight out of the box LaTeX uses the definitions that are in the file fontmath.ltx and there you will find for \mathbf:

\DeclareMathAlphabet      {\mathbf}{OT1}{cmr}{bx}{n}


In other words: Computer Modern bold extended.

-
I would argue with you. This is the definite answer! Because at whatever LaTeX installation you check the mentioned file, you see the font name. –  yo' Feb 24 '12 at 16:20
@tohecz not sure what you think there is to argue. It is the definite answer what LaTeX does out of the box, but LaTeX is not forced to do this, e.g., if you load txfonts then your math is typeset in Times (some sort of it anyway) or if you load eulervm mathbf may point to Concrete bold, etc. –  Frank Mittelbach Feb 24 '12 at 16:51

That font is is Computer Modern Bold Extended by default. You can check it if you open the produced PDF document in your reader and look at the document properties and the used fonts, or use the pdffonts tool. With a simple article document without packages or options, you would see CMBX10.

If you use some packages and see another font name, have a look here:

Or locate the name in your TeX file system or just type it into a search engine for finding the human readable name for an abbreviation.

-