# How to make the letter “K” that denote Krylov space

I'm trying to denote the letter K that appear in notation Krylov Space

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

• if you have a pdf of that (eg google suggested sam.math.ethz.ch/~mhg/pub/biksm.pdf) you can list the fonts it uses (just standard computer modern and ams fonts in that case) – David Carlisle Jun 8 at 15:48
• Welcome to the TeX.SE. What package are you using? – Sebastiano Jun 8 at 15:49
• For my humble opinion the K of your picture is the same of \mathcal{K}. – Sebastiano Jun 8 at 16:06
• You are probably doing \usepackage{mathptmx}, Look at my edited answer. – egreg Jun 8 at 16:27

It's the standard \mathcal{K}.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

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

\end{document}


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}


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}


looks a bit like kappa from txfonts, just a bit bigger:

\documentclass{article}

\usepackage{graphicx}
\usepackage{mathtools}
\usepackage{txfonts}

\begin{document}

$\text{\scalebox{1.4}{\kappa}}(r_0)$

\end{document}


• Why downvote? This seems to be a valid answer! – pushpen.paul Jun 9 at 15:25