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Subscripts actually under a union of sets sign

Peter

Well-known member
MHB Site Helper
Jun 22, 2012
2,918
I recently made a post on Linear and Abstract Algebra and used the following symbol

\(\displaystyle {\bigcup}_{\Omega \subseteq \Gamma , | \Omega | \lt \infty} \)

However, I really wanted (for neatness and clarity) to have the term \(\displaystyle {\Omega \subseteq \Gamma , | \Omega | \lt \infty} \) actually under the set union symbol as in the commutative algebra text by R.Y. Sharp - see attachment page 7 exercise 1.12.

Can someone please help in this matter?

Peter
 

Jameson

Administrator
Staff member
Jan 26, 2012
4,040
I recently made a post on Linear and Abstract Algebra and used the following symbol

\(\displaystyle {\bigcup}_{\Omega \subseteq \Gamma , | \Omega | \lt \infty} \)

However, I really wanted (for neatness and clarity) to have the term \(\displaystyle {\Omega \subseteq \Gamma , | \Omega | \lt \infty} \) actually under the set union symbol as in the commutative algebra text by R.Y. Sharp - see attachment page 7 exercise 1.12.

Can someone please help in this matter?

Peter
Hmm, let's see if this works...

\(\displaystyle \underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}\)

It does! Here you go:

\underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}
 

Peter

Well-known member
MHB Site Helper
Jun 22, 2012
2,918
Hmm, let's see if this works...

\(\displaystyle \underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}\)

It does! Here you go:

\underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}
Thanks Jameson, appreciate the help

Peter
 

Evgeny.Makarov

Well-known member
MHB Math Scholar
Jan 30, 2012
2,492
If subscripts and superscripts of big operators are typeset below and above the operator, they are referred to as limits. Whether TeX uses limits depends on whether the formula is in display style (limits are used) or text style (normal sub- and superscipts are used). By default, inline formulas beginning with \( and $ are typeset in text style, while those beginning with \[ and $$ use display style. (Note that $$ is deprecated, at least in PDF documents.) The tags [math]...[/math] on this site apparently create an inline formula but use display style. The style determines many other parameters besides whether to use limits; most noticeable are the size of operators and fractions.

You used the [math] tag, so the formula is in display style, but you enclosed \bigcup in curly braces. This turned it into a generic subformula and TeX did not take into account that inside is a big operator, which treats subscripts in a special way. That's why the subscript was not made into a limit.

Without changing the position of a formula (display or inline), its style can be modified using \displaystyle and \textstyle commands. Independently of this, you can type \limits or \nolimits immediately after a big operator to direct TeX to use limits or not.

Edit: See this thread for examples of formulas in display style and text style.

Edit 2: The info above relates to big operators (in TeX terminology) like \bigcup. The command \underset can be used in other contexts.
 
Last edited:

Jameson

Administrator
Staff member
Jan 26, 2012
4,040
Interesting and good to know, Evgeny.Makarov! I'll test this out.

Here is without putting \bigcup in curly brackets:

\(\displaystyle \bigcup_{\text{testing if this works}}\)

And here is with curly brackets:

\(\displaystyle {\bigcup}_{\text{testing if this works}}\)

Yep, this way is much faster than my solution. :D
 

Peter

Well-known member
MHB Site Helper
Jun 22, 2012
2,918
If subscripts and superscripts of big operators are typeset below and above the operator, they are referred to as limits. Whether TeX uses limits depends on whether the formula is in display style (limits are used) or text style (normal sub- and superscipts are used). By default, inline formulas beginning with \( and $ are typeset in text style, while those beginning with \[ and $$ use display style. (Note that $$ is deprecated, at least in PDF documents.) The tags [math]...[/math] on this site apparently create an inline formula but use display style. The style determines many other parameters besides whether to use limits; most noticeable are the size of operators and fractions.

You used the [math] tag, so the formula is in display style, but you enclosed \bigcup in curly braces. This turned it into a generic subformula and TeX did not take into account that inside is a big operator, which treats subscripts in a special way. That's why the subscript was not made into a limit.

Without changing the position of a formula (display or inline), its style can be modified using \displaystyle and \textstyle commands. Independently of this, you can type \limits or \nolimits immediately after a big operator to direct TeX to use limits or not.

Edit: See this thread for examples of formulas in display style and text style.

Edit 2: The info above relates to big operators (in TeX terminology) like \bigcup. The command \underset can be used in other contexts.
Thanks Evgeny

A most informative post!

Peter