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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?

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  • Related: How to place a \mathcal{D} below the text "err"
    – user11232
    Commented Nov 5, 2015 at 8:22
  • 1
    Should the \Delta symbol be larger in displaystyle mode than in textstyle, scriptstyle, and scriptscriptstyle math mode? Please advise.
    – Mico
    Commented Nov 5, 2015 at 8:37

2 Answers 2

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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}

enter image description here

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  • Thank you and Harishu Kumar. These are exactly what I want.
    – ganganray
    Commented Nov 29, 2015 at 8:50
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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}

enter image description here

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