3

This is a trivial question. We know that in the table 72: Variable-sized Math Operators to the pag. 40, we have the symbol for the line integral of a closed path named \oint for the circuiting.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\begin{document}
Table 72: Variable-sized Math Operators pag. 40.
\[\oint\]
\end{document}

But the high school students are not familiar with this symbol and I have thought of to use the symbol of the sum with the circle inside. But this symbol is only declared in stix fonts (see to pag. 46 \modtwosum).

enter image description here

If I should use mtpro2[lite] (that use the font Times New Roman) or the classic amssymb I should overlapping the two symbols of summation and the small circle in the center or can I find a more effective or best strategy?

Any kind of suggestions are appreciated.

Sebastiano
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    You might try doing that with \stackinset command from the stackengine package. – Bernard Mar 27 '21 at 22:33
  • @Bernard Very kind Bernard, I was putting it in the tags :-)) thank you very much for the suggestion. – Sebastiano Mar 27 '21 at 22:35
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    This being said, do you really think a high-school student in not able to understand the \oint symbol, if it is explained? – Bernard Mar 27 '21 at 22:43
  • @Bernard There is a real reason. When using approximations for integrals we use the summation symbol. In high school Physics books the symbol for circuiting is used with \oint. In order to avoid sterile controversy with those who are not proficient prof. in math and physics and think they are, especially in my school, instead to use $C_{\gamma}(\mathbf{E})$ I would like to use the summation symbol with the circle. I'm just telling you that most students don't even know how to use a calculator, and I'm really unhappy about this. – Sebastiano Mar 27 '21 at 22:48
  • I see. Note that, when I was a high schooler, calculators did not exist, but was taught (at 11!) how to calculate a square root by hand, with a method similar to long division – just a bit more complex. – Bernard Mar 27 '21 at 22:52
  • @Bernard So I'm getting older in age too. I have a book where there is a method to calculate square roots by hand by dividing the number into groups of two with a point. I never used it when I was 11 because it wasn't in the math textbooks, but I discovered it around 25, 26 years of age. I've forgotten how to do it by now and should review the mechanism. – Sebastiano Mar 27 '21 at 22:58
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    It's just a tricky use of the formula $(a+b)^2=\dots$. Later I discovered that the mathematical justification was given as a problem for a competitive exam for an engineer school… – Bernard Mar 27 '21 at 23:04
  • @Bernard I do not know the trick but I could ask a question on MSE community :-) – Sebastiano Mar 27 '21 at 23:09
  • It's easier to explain from an example on a black board. Roughly, the expansion of $(a+b)^2$ is written as $a^2 + (2a+b)\cdot b$. – Bernard Mar 27 '21 at 23:15
  • If you can use unicode-math, several fonts have it, including XITS, STIX Two and New Computer Modern. – Davislor Mar 28 '21 at 02:04
  • @Davislor Hi kindest. I not like much the unicode-math. I like innovations, but on some things I am a traditionalist. :-) – Sebastiano Mar 28 '21 at 11:29
  • @Sebastiano You can have a look at https://tex.stackexchange.com/a/46389/4427 – egreg Mar 28 '21 at 14:34
  • @egreg Kindest Enrico. No otherwise I wouldn't have asked the question. My question, in all sincerity, is therefore a duplicate and should be closed. I thank you for the information. My besttttt regards. – Sebastiano Mar 28 '21 at 19:54

2 Answers2

2

You could also borrow the symbol from STIX without loading the whole font.

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\DeclareFontEncoding{LS2}{}{\noaccents@}
\DeclareFontSubstitution{LS2}{stix}{m}{n}
\DeclareSymbolFont{largesymbols}  {LS2}{stixex}   {m} {n}
\DeclareMathSymbol{\modtwosumop}            {\mathop}{largesymbols}{"C4}
\def\modtwosum{\DOTSI\modtwosumop\slimits@}
\makeatother
\begin{document}
\( \displaystyle \modtwosum_{i=1}^n a_i \)
\( \modtwosum_{i=1}^n a_i \)
\( \scriptstyle \modtwosum_{i=1}^n a_i \)
\( \scriptscriptstyle \modtwosum_{i=1}^n a_i \)
\end{document}

Vincent
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  • In my humble opinion the two responses are equivalent. So to be fair I will not put a green check mark as I have done on other occasions but will thank otherwise. – Sebastiano Mar 28 '21 at 19:51
1

The following defines an \osum that is just an overlayed \circ and \sum with some manually applied spacing.

\documentclass[a4paper,12pt]{article}
\usepackage{graphicx}
\usepackage{amsmath,amssymb}

\makeatletter
\newcommand*\osum
  {%
    \mathop
      {%
        \mathchoice
          {%
            \rlap
              {%
                $\displaystyle
                \mkern9mu
                \raisebox{-.1\height}{\scalebox{1.2}{$\displaystyle\circ$}}$%
              }%
          }%
          {\rlap{$\textstyle\mkern6.3mu\circ$}}%
          {\rlap{$\scriptstyle\mkern6.5mu\circ$}}%
          {\rlap{$\scriptscriptstyle\mkern5.5mu\circ$}}%
        \sum
      }%
    \slimits@
  }
\makeatother


\begin{document}
Table 72: Variable-sized Math Operators pag. 40.
[\oint]
[\osum]
${\displaystyle\osum}\osum_{\osum_{\osum}}$
\end{document}

enter image description here

Skillmon
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