Crthuky

How can I write a square version of the integral sign? I'm looking for something that has the same height as a regular integral sign and looks like this:

Note that this symbol is not found by Detexify and does not appear to be in the comprehensive list of symbols.

You can always build your own symbol. (If you want such integrals also to show up as subscripts, you need to add the corresponding code to the last options of mathchoice.)

documentclassarticle
usepackageamsmath
usepackagetikz
DeclareMathOperator*SquareIntmathchoicetikz[baseline=0.55em]%
draw[line width=0.08em] (-0.2em,0em) 
tikz[baseline=0.35em]- (0,-0.2em) -- (0,1.2em) -
begindocument
[ SquareIntlimits_a^bf(x),mathrmdxquadtextvs.quad 
intlimits_a^bf(x),mathrmdx]
$SquareIntlimits_a^bf(x),mathrmdxquadtextvs.quad 
intlimits_a^bf(x),mathrmdx$
enddocument

You can design your own using rules. This solution measures the height and depth of the integral to ensure exact size.

Here is the code:

documentclassarticle

usepackagecalc % needed to add lengths 
usepackageamsmath % needed for DeclareMathOperator

newlengthhght
newlengthdpth

DeclareMathOperatorsqrintmathchoice%
settoheighthght$displaystyleint$settodepthdpth$displaystyleint$% measures int
 rule[-dpth].2ex.5ex% lower vert
 rule[-dpth].12em.2ex% lower hor
 rule[-dpth].2exhght+dpth% main vert
 rule[hght-.2ex].12em.2ex% upper hor
 rule[hght-.5ex].2ex.5ex% upper vert
settoheighthght$int$settodepthdpth$int$%
 rule[-dpth].15ex.4ex%
 rule[-dpth].1em.15ex%
 rule[-dpth].15exhght+dpth%
 rule[hght-.15ex].1em.15ex%
 rule[hght-.4ex].15ex.4ex%
settoheighthght$scriptstyleint$settodepthdpth$scriptstyleint$%
 rule[-dpth].1ex.3ex%
 rule[-dpth].08em.1ex%
 rule[-dpth].1exhght+dpth%
 rule[hght-.1ex].08em.1ex%
 rule[hght-.3ex].1ex.3ex%


begindocument

Inline square integral: $int_0^1sqrint_0^1$, subscripted: $A_int_0^1sqrint_0^1$, or a displayed version:
[
int_0^1sqrint_0^1
]

enddocument

Note that I have not added the code for a scriptscript version. You can adjust the lengths and thicknesses as you wish.