math-modemath-operators
This question is in connection with How to typeset function restrictions
There, egreg gives a satisfactory answer (at least for me)
The problem is that I'd like to do the same thing with \restriction as delimiter instead of |, but somehow I can't figure out how to do that.
One possibility: I used \DeclarePairedDelimiterX from the mathtools package to define a \MeijerM command with three arguments which is responsible to typeset the delimited matrix; then I defined \MeijerG having eight arguments (the first one is optional and will be passed as the optional argument to \MeijerM); using the \WithSuffix command from the suffix package to provide the starred version \MeijerG*:
\documentclass[11pt]{article}
\usepackage{suffix}
\usepackage{mathtools}
\DeclarePairedDelimiterX\MeijerM[3]{\lparen}{\rparen}%
{\begin{smallmatrix}#1 \\ #2\end{smallmatrix}\delimsize\vert\,#3}
\newcommand\MeijerG[8][]{%
G^{\,#2,#3}_{#4,#5}\MeijerM[#1]{#6}{#7}{#8}}
\WithSuffix\newcommand\MeijerG*[7]{%
G^{\,#1,#2}_{#3,#4}\MeijerM*{#5}{#6}{#7}}
\begin{document}
\[
\MeijerG*{m}{n}{p}{q}{a_1, \dots, a_p}{b_1, \dots, b_q}{z}\quad
\MeijerG[\big]{m}{n}{p}{q}{a_1, \dots, a_p}{b_1, \dots, b_q}{z}\quad
\MeijerG[\Bigg]{m}{n}{p}{q}{a_1, \dots, a_p}{b_1, \dots, b_q}{z}
\]
\end{document}
The size of delimiters in the second and third examples is obviously wrong, but I just included them to test the functionality of the defined commands. Also, I used simple sub/superscripts to typeset the first four arguments, but of course you can use one of your proposed variants instead.
First, let me give a paraphrasing from The TeXbook showing the amounts of spaces between different types of math atoms:
where
Ord includes things like a, \theta, and things inside \mathord or just plain {}'s;Op includes things like \sin, \gcd, and things inside \mathop;Bin includes things like \pm, \otimes, and things inside \mathbin;Rel includes things like \leq, \mid, and things inside \mathrel;Open includes things like \langle, (, and things inside \mathopen;Close includes things like \rangle, ), and things inside \mathclose;Punct includes things like ,, ., and things inside \mathpunct;Inner includes things like \cdots and things inside \mathinner.Here is an example plain-tex document illustrating a couple of different ways:
\let\funarg\mathinner
\def\funop#1{\mathop{{}#1}}
$$ i(x,y,z,t) = \delta(x-\ell_x(z)) \delta(y-\ell_y(z)) \hat\imath(\xi(z),t), $$
$$ i\funarg{x,y,z,t} = \delta\funarg{(x-\ell_x(z))} \delta\funarg{(y-\ell_y(z))} \hat\imath\funarg{(\xi(z),t)}, $$
$$ \funarg{i(x,y,z,t)} = \funarg{\delta(x-\ell_x(z))} \funarg{\delta(y-\ell_y(z))} \funarg{\hat\imath(\xi(z),t)}, $$
$$ \funop i(x,y,z,t) = \funop\delta(x-\ell_x(z)) \funop\delta(y-\ell_y(z)) \funop{\hat\imath}(\xi(z),t), $$
\bye
So as you can see, you probably want the last option of using a \mathop atom for the function "name".
With LaTeX, this could be defined as follows (the second row below shows the output of your original code):
\documentclass{article}
\newcommand\funop[1]{\mathop{{}#1}}
\begin{document}
$i(x,y,z,t) = \funop\delta(x-\ell_x(z)) \funop\delta(y-\ell_y(z)) \funop{\hat\imath}(\xi(z),t)$
vs.
$i(x,y,z,t) = \delta(x-\ell_x(z)) \delta(y-\ell_y(z)) \hat{\imath}(\xi(z),t)$
\end{document}
(The reason I didn't include the parenthesis in the command is that I felt it would be too much effort to measure the arguments to decide on the size of the fences. I think it's simpler to just manually define the height with \bigl( etc., and also it's nicer to see the parens in the manuscript instead of {}'s)
Best Answer
You can say (requires
amssymb, of course)and the result will be as in the second line in the following picture, while the first line represents what you get now