# [Tex/LaTex] Palatino, roman \chi and the math mode

fontskoma-scriptmath-modesymbols

I am using Palatino for the content and I have a problem displaying \chi in math mode. The problem happens when I have a roman formatting in math, e.g., vector x, X, and χ; the χ turns to some other character.

## The minimal example

\documentclass[12pt,oneside,english,titlepage, a4paper, fontsize=12pt]{scrbook}

\usepackage{mathpazo}
\usepackage{geometry}
\geometry{letterpaper}
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{epstopdf}

%show vectors in bold
\renewcommand\vec[1]{\mathrm{\mathbf{#1}}}
%end renew commands

\title{Brief Article}
\author{The Author}
\begin{document}

\noindent Three different systems of reference are used within this
work. Structural deformations are described in the Lagrangian or material
formulation. The corresponding Lagrangian coordinate system denoted
by $\vec{X}$ is associated with the particular material points. The Eulerian or
spatial system of reference denoted by $\vec{x}$,
in which the observer is fixed in space and looks at the fluid passing.
In the ALE description of the motion, a third reference system, denoted
by $\vec{\chi}$.
\end{document}


which produces the following image:

What I would like to have is this [1]:

How can I fix this?

[1] The difference is that I removed \usepackage{mathpazo} from the top.

As long as your vectors are only Roman or Greek letters, the following works

\usepackage{bm}

%show vectors in bold
\DeclareRobustCommand\vec[1]{%
\ifcat\noexpand#1\relax
\expandafter\bm
\else
\expandafter\mathbf
\fi{#1}}
%end renew commands


Your \mathrm serves no purpose. The problem is that there's no Greek letter in the font used by \mathbf, so we resort to the \bm macros of package bm.

Caution This works only with one letter as the argument.

An alternative can be simply

\usepackage{bm}
\renewcommand{\vec}{\bm}


but Roman letters will be in boldface (math) italic.