Summation Symbol

Question

Want to write a summation symbol in the similar form in the attachment. Please advice.

Answer 1

\documentclass[]{article}

\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{calc}
\newlength{\depthofsumsign}
\setlength{\depthofsumsign}{\depthof{$\sum$}}
\newlength{\totalheightofsumsign}
\newlength{\heightanddepthofargument}

% https://tex.stackexchange.com/questions/22773/making-a-big-summation-sign
\newcommand{\nsum}[1][1.4]{
  \mathop{%
    \raisebox
    {-#1\depthofsumsign+1\depthofsumsign}
    {\scalebox
      {#1}
      {$\displaystyle\sum$}%
    }
  }
}

\begin{document}

\[
\sum_k^n \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix} = \nsum[2]_k^n \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}
\]

\end{document}

Answer 2

Here are two further solutions:

• Instead of enlarging the summation symbol, shrink the matrix, by using a psmallmatrix environment instead of a pmatrix environment.

• Load the relsize package and employ \larger instructions to enlarge the size of the \sum symbol. In the code below, I create a macro called \bigsum. By default, the applies \larger three times, for a total magnification of (1.2)^3=1.728. (Doubling the \sum symbols seems excessive to me...)

The following code also re-implements the \nsum macro shown in @caverac's answer, so that TeX does all the hard work, mainly via a \vcenter instruction. This seems nicer than performing several length calculations and then employing a \raisebox instruction.

\documentclass{article}

\usepackage{mathtools} % for 'pmatrix' environment
\usepackage{relsize}   % for '\larger' macro
\usepackage{graphicx}  % for '\scalebox' macro

\newcommand\nums{0 & 1 \\ 1 & 0} % handy shortcut macro

% default enlargement applied by `\bigsum`: 3 steps of 1.2 
\newcommand\bigsum[1][3]{\mathop{\vcenter{\hbox{%
   \larger[#1]{$\displaystyle\sum$}}}}}

% reimplementation of '\nsum': make TeX do all the hard work
\newcommand{\nsum}[1][1.44]{\mathop{\vcenter{\hbox{%   % 1.44=(1.2)^2
   \scalebox{#1}{$\displaystyle\sum$}}}}}

\begin{document}
\[
  \sum_k^n    \begin{psmallmatrix} \nums \end{psmallmatrix}
= \sum_k^n         \begin{pmatrix} \nums \end{pmatrix}
= \bigsum_k^n      \begin{pmatrix} \nums \end{pmatrix}
= \nsum[1.728]_k^n \begin{pmatrix} \nums \end{pmatrix}  % 1.728=(1.2)^3
\]

\end{document}

Answer 3

In unicode-math, you can load another copy of a math font with the scale= parameter to increase the size of a math symbol. This would be wrapped in several different macros to insert the glyph from text mode and treat it as a math operator with limits above and below. Based on suggestions in the comments, this also centers the symbol vertically and sets the font to Cambria Math, although scaled Cambria Math gives a summation symbol that’s thicker than you wanted.

\documentclass[varwidth, preview]{standalone}

\usepackage{amsmath}
\usepackage{unicode-math}

\setmainfont{Cambria}
\setmathfont{Cambria Math}
\newfontface\bigmath{Cambria Math}[Scale=3.0]

\newcommand\bigsum{\mathop{\vcenter{\hbox{\bigmath ∑}}}\limits}

\begin{document}
\(
  \bigsum_k^n \begin{pmatrix}0&1\\1&1\end{pmatrix}
\)
\end{document}

You could vary the scale= parameter using the font features commands from fontspec, although if you want a specific height, you probably want a \resizebox from graphicx.