How can I define a new operator, which works the same as sum, prod in both inline and display math mode?

Question

I want to define a new operator say \Delta . Which works as the same as \sum or \prod in both in line and display math mode. Say, the subscribes is to the right of the operator in the in line mode, and under the operator in the display mode. How can we do this?

Should the \Delta symbol be larger in displaystyle mode than in textstyle, scriptstyle, and scriptscriptstyle math mode? Please advise. — Mico, Nov 05 '15 at 08:37

score 9 · Answer 1 · answered Nov 05 '15 at 08:17

You can do it with \DeclareMathOperator* provided by amsmath. Refer to amsmath manual, page 17 for more details.

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator*{\Del}{\Delta}
\begin{document}
  $\Del_x^y=0$
  \[\Del_x^y=0\]
\end{document}

score 7 · Accepted Answer · answered Nov 05 '15 at 11:29

7

If you want it to be literally the size of \sum, then this twist will scale the \Delta to match the vertical footprint of \sum.

\documentclass{article}
\usepackage{amsmath,scalerel}
\DeclareMathOperator*{\Del}{\scalerel*{\Delta}{\sum}}
\begin{document}
  $\Del_{i=0}^n x_i=0$
  \[\Del_{i=0}^n x_i=0\]
\end{document}

answered Nov 05 '15 at 11:29

Steven B. Segletes

237,551

Thank you and Harishu Kumar. These are exactly what I want. – ganganray Nov 29 '15 at 08:50

How can I define a new operator, which works the same as sum, prod in both inline and display math mode?

2 Answers2

Linked