[Tex/LaTex] why textbf doesn’t work when writing between dollar signs between the curly brackets

bold

I'm trying to write the following but in bold: $M_s$ so that the "s" becomes next to "M" but low and i have the following code:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{tikz}
\title{Fundamentals of informatics A4}
\author{some name}
\date{January 2018}

\setlength{\parindent}{0pt}
\begin{document}
% some text

into a new Turing machine \textbf{$M_s$} with the following behavior:

%some more text

\end{document}

The problem is that the M_s wouldn't appear bold no matter what i try

edit1: \textbf{} works perfectly with just text but when using the dollar signs, it doesn't.

Best Answer

Use the bm package and type $\bm{M_s}$ to get what you want. The command \textbf is for ordinary text, not for mathematical text.

Related Solutions

[Tex/LaTex] Why doesn’t the ‘bm’ package work with the ‘unicode-math’ package

First, some general comments and observations about the code shown in your preamble:

When using LuaLaTeX or XeLaTeX, you should not load the fontenc and inputenc packages. (Even when using pdfLaTeX, it's no longer necessary to load the inputenc package unless your file's input encoding is not UTF8 or ASCII, which is a proper subset of UTF8.)
Loading the colortbl and color packages independently is a mistake, as it doesn't maximize the compatibility and interoperability of these two packages. Hence, do replace \usepackage{color, colortbl} with \usepackage[table]{xcolor}. See section 2.1.2, "Package options", as well as Table 1, "Package options", of the user guide of the xcolor package for more information.
When using the unicode-math package along with a suitable OpenType math font (specified via a suitable \setmathfont instruction), there's no need to load the following packages: lmodern, fontspec, amsmath, amsfonts, amssymb, and bm. (Aside: If you load the unicode-math package but do not run a \setmathfont directive, the default math font is Latin Modern Math.)
The unicode-math package loads the amsmath package automatically if it hasn't already been loaded prior to LaTeX encountering the instruction \usepackage{unicode-math}. See Section 3, "Getting Started", of the user guide of unicode-math package for more information.
If you wish to use the \mathscr directive of the mathrsfs package, be sure to load mathrsfs after unicode-math. (I mention this because the preamble you posted loads the mathrsfs package.)

Now, finally, to the main part of your query:

I want the bold italic math character (as in normal math) in math mode

To generate bold italic math-mode letters and symbols, the unicode-math package provides a macro called \symbfit. Use it in lieu of \boldsymbol and \bm. (As you've discovered, \bm doesn't work anyway; hence, don't use it.)
To generate bold upright math-mode letters and symbols, use \symbfup. Use it in lieu of \mathbf.

As the following screenshot demonstrates, \symbfit and \symbfup -- as well as their regular-weight counterparts \symit and \symup -- affect the weight and shape of Latin and Greek letters, but not the shape and weight of (math) "operators" such as \int, \sum, \exp, and \ln.

\documentclass{book}
\usepackage{unicode-math}
\setmainfont{Latin Modern Roman} 
\setmathfont{Latin Modern Math}

\newcommand\blurb{(\sqrt[n]{x}\,)^{n}=\sqrt[n]{x^{n}}=x 
     \quad \alpha\beta\Sigma\Omega \quad \int\sum\exp\ln}

\usepackage{setspace}  % just for this example
\setstretch{1.25}

\begin{document}
\obeylines
$\blurb$ --- default
$\symbfit{\blurb}$ --- \verb+\symbfit+
$\symbfup{\blurb}$ --- \verb+\symbfup+
$\symit{\blurb}$ --- \verb+\symit+
$\symup{\blurb}$ --- \verb+\symup+
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Why doesn’t the ‘bm’ package work with the ‘unicode-math’ package

Related Question