In Oliver Salazar Celis' "Adaptive Thiele interpolation," ACM Communications of Computer Algebra 56(3), Issue 221, September 2022, page 125 (Eq. 1) we find:

ACM equation

How does one typeset the vertical plus horizontal notation (note that the straight segments touch)?

And what does this notation mean?

  • 1
    This looks like a continued fraction.
    – projetmbc
    May 24 at 18:44
  • 1
    Google or others give: "an algorithm generates a Thiele-Werner continued fraction representation of the interpolant".
    – projetmbc
    May 25 at 8:40

2 Answers 2


A simple array could do the trick, but I have no idea about what it means. First time I see something like that.

Update: added the array package for better rules connections, as suggested in the comments.

\usepackage{array} % better connections between the rules (see egreg's comment)


C_n(x) = \varphi_0[x_0] + \myfrac{x-x_0}{\varphi_1[x_0,x_1]} +
                          \myfrac{x-x_1}{\varphi_2[x_0,x_1,x_2]} +
                          \myfrac{x-x_2}{\cdots} +

enter image description here

  • 2
    Perfect. Thanks. (accept) Now I'll post on math.SE to see what it means! May 24 at 18:34
  • 3
    @DavidG.Stork you will need \newcommand not \NewDocumentCommand for mathjax. May 24 at 20:57
  • 1
    You should also load array in order to improve the connections between the rules.
    – egreg
    May 25 at 10:08
  • @egreg, done!! Thanks for pointing it. May 25 at 10:49

Using holtpolt package.


\[C_n(x) = \varphi_0[x_0] +\polter{x-x_0}{\varphi_1[x_0,x_1]}+\polter{x-x_1}{\varphi_2[x_0,x_1,x_2]}+\polter{x-x_2}{\ldots}+\polter{x-x_{n-1}}{\varphi_n[x_0,\ldots,x_n]}\]

enter image description here


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