Cfrgtkky

I want to have a cup command that adapts to the size of an array on its left (Something like left and right for the parenthesis), while keeping the same font for the letters and the thickness of the line. I tried using bigcup with the scalerel package but the line and the subscript become too wide. I report here a minimal example to show what is the result:

documentclass{article}

usepackage{scalerel}

begin{document}

[

scalerel{

      bigcuplimits_{x in X}

}

{

    left{

       f(x) 

       begin{array}{| l}

           a \ % first row

           b \ % second row

           c \ % third row

           d \ % fourth row

           e \ % fifth row

           dots \ % etc.

           z \ % n-th row

       end{array}

    right}

}

]

end{document} 

The size obtained is the right one, however the size of font x in X becomes too big and the line too thick.

How can I have a similar result without these distortions?

I think scaling with the array size you will always be up against the fact that the entire contents of the scalerel box, including the subscript, are scaled, leading to inconsistent script sizes (and probably ridiculously size cups as well).

I would suggest instead using the scaleobj command also provided by the scalerel package, which functions similar to scalebox from the graphicx package. While scaling up the entire cup plus subscript, you can scale the subscript alone in the other direction. To get the subscript sitting nicely under the cup after the inner scaling, a raisebox and smash can be added:

documentclass{article}

usepackage{scalerel}

newcommandhugecup{%

    scaleobj{2.5}{%

        bigcuplimits_{smash{raisebox{.25baselineskip}{(scaleobj{0.425}{xin X})}}}

    }

}

begin{document}

[

hugecup

    left{

       f(x) 

       begin{array}{| l}

           a \ % first row

           b \ % second row

           c \ % third row

           d \ % fourth row

           e \ % fifth row

           dots \ % etc.

           z \ % n-th row

       end{array}

    right} 

]

end{document}

Output:

The values used are just what I thought looked sensible for a range of different (large) arrays; you may wish to tweak these.