Complex Fractions in LaTeX

[topsquark]

TL;DR Summary

Exploring different ways to represent a complex fraction using LaTeX

I know of two reasonable ways to represent a complex fraction:
\dfrac{ \left ( \dfrac{a}{b} \right ) }{ \left ( \dfrac{c}{d} \right ) }
$\dfrac{ \left ( \dfrac{a}{b} \right ) }{ \left ( \dfrac{c}{d} \right ) }$

and
\dfrac{ ^a / _b }{ ^c / _d }
$\dfrac{ ^a / _b }{ ^c / _d }$

What I am wondering is if there is a way to write
$\dfrac{ \dfrac{a}{b} }{ \dfrac{c}{d} }$
by making a longer middle division line?

Thanks!

-Dan

 

[I like Serena]

Hey Dan,

One way to make the middle line longer, is to add latex spaces to numerator or denominator.
For instance:
\dfrac{\;\dfrac ab\;}{\dfrac cd}
$\dfrac{\;\dfrac ab\;}{\dfrac cd}$

 

[berkeman]

add latex spaces to numerator or denominator

Sometimes I have to add explicit "~" characters to force spaces in LaTeX, but other times just " " spaces seem to work. I haven't figured out why yet...

 

[Orodruin]

Sometimes I have to add explicit "~" characters to force spaces in LaTeX, but other times just " " spaces seem to work. I haven't figured out why yet...

Can you give some examples?

 

[I like Serena]

Sometimes I have to add explicit "~" characters to force spaces in LaTeX, but other times just " " spaces seem to work. I haven't figured out why yet...

Regular spaces are generally used as separator. For instance in \dfrac ab the space is not an actual space, but instead it's a separator. That separator only "becomes" a space, if that is needed to separate both sides. In that case multiple spaces are collapsed to a single space.
If we actually "want" a space where that is not already natural, we have to use one of the latex spaces like:
\! \, \: \; \quad \qquad, which are increasingly wide spaces. The first one is a negative space. The "~" is special in that it creates a non-breaking space, so that it won't "wrap".

 

[berkeman]

Can you give some examples?

Just a quick example:
$$v(t) = L \frac{di(t)}{dt}$$
$$v(t) = L~\frac{di(t)}{dt}$$
from:

 

[I like Serena]

The classical example is an integral: $$\int f(x,y) dx dy$$
Often \, is inserted (despite already having spaces) before the infinitesimals to get a more natural formula:$$\int f(x,y)\,dx\,dy$$
A "~" also works of course.

 

[Orodruin]

Just a quick example:
$$v(t) = L \frac{di(t)}{dt}$$
$$v(t) = L~\frac{di(t)}{dt}$$
from:
View attachment 313827

I meant examples of where you would expect a space but there was none.

A "~" also works of course.

Compare the following:
$$
\int f(x,y)~dx~dy \qquad \int f(x,y)\,dx\,dy
$$
The non-breaking space ~ is a regular sized space (it is equivalent in size to the regular \ ) as compared to \, which is 3 mu. The latter is typically what you want. The non-breaking space ~ should be used when you have a space where you do not wish to create a (line or page) break. In an equation it is essentially equivalent to the regular space "\ " (which has its own uses in text as well, such as not creating a too large space after an abbreviation, i.e., LaTeX will interpret "cf. last chapter" as there being an end of sentence after cf. whereas "cf.\ last chapter" will not).

 

[berkeman]

I meant examples of where you would expect a space but there was none.

In the first LaTeX line, I put a " " space after the L, but it did not render. It took the explicit "~"space after the L to get it to render.

 

[Orodruin]

In the first LaTeX line, I put a " " space after the L, but it did not render. It took the explicit "~"space after the L to get it to render.

Of course it didn’t, spaces are mostly irrelevant to math mode (for good reason).

 

[Wrichik Basu]

For integrals, using the physics package might be helpful to some extent. One may use \dd{} from that package, which manages the spacing automatically, and also makes the d upright.
$$\require{physics}
\int f(x,y) \dd{x} \dd{y}$$