[Tex/LaTex] How to make the letter “K” that denote Krylov space

characters

I'm trying to denote the letter K that appear in notation Krylov Spaceenter image description here

I've already tried to use \mathcal and \kappa but it's not the same.

Best Answer

It's the standard \mathcal{K}.

enter image description here

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
\mathcal{K}(r_0;k)=\operatorname{span}\{r_0,Ar_0,\dots,A^kr_0\}
\]

\end{document}

enter image description here

I guess that your document uses mathptmx. Do like this:

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathptmx}

\DeclareMathAlphabet{\mathcal}{OMS}{cmsy}{m}{n}

\begin{document}

\[
\mathcal{K}(r_0;k)=\operatorname{span}\{r_0,Ar_0,\dots,A^kr_0\}
\]

\end{document}

enter image description here

If you're using newtx, the code should be

\documentclass{article}
\usepackage{amsmath}
\usepackage{newtxtext,newtxmath}
\usepackage{fix-cm}

\DeclareMathAlphabet{\mathcal}{OMS}{cmsy}{m}{n}

\begin{document}

\[
\mathcal{K}(r_0;k)=\operatorname{span}\{r_0,Ar_0,\dots,A^kr_0\}
\]

\end{document}
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