amsmathfractionsxfrac
I want a fraction of derivatives, so I use this code:
\documentclass{article}
\usepackage{amsmath}
\usepackage{xfrac}
\begin{document}
Good: $\sfrac{4}{5}$
Not good: $ \sfrac{\dfrac{dy}{dt}}{\dfrac{dx}{dt}} $
\end{document}
As you can see, the result is not very beautiful:
At the first fraction 4 is in a higher level than 5. But it is the opposite at the second fraction.
How can I solve this problem?
Thanks in advance!
Given the lack of answers other than the comments, here is a summary of the critiques which have come from the comments. By increasing the visibility of these comments, I'm hoping that I may get a solution to the portability problem noted so far, and provoke further critiquing of my macro generally.
Technical/æsthetic obstacle:
Brent.Longborough, with further elaboration by TH., noted that this macro is not necessarily very robust to a change in font, which may have different dimensions for e.g. its ex-size relative to the size of the actual letters. It would seem that a different choice of parameters in the \raisebox-es, and possibly the \scalefont-s as well, may be necessary for each different font used.
Technical improvement:
TH. suggested (if I understand correctly) that I should modify the macro using \m@th (or equivalent): a little research indicates that this is probably to improve the horizontal spacing of the result. Thus, a minor improvement would be
\makeatletter
\newcommand\sfrac[2]{% \dfrac{\text{\raisebox{-0.5ex}{\scalefont{0.85}{$\m@th#1$}}}}% {\text{\raisebox{0.35ex}{\scalefont{0.85}{$\m@th#2$}}}}% }
\makeatother
[EDIT: I am 'accepting' this answer for now, but if anyone comes along and provides useful insights, I will change the accepted answer.]
Probably you had added \displaystyle to get the superscript and subscript of the inner sum operator on top and below the symbol. This also increases the size of the fraction. Instead \limits can be used to move the superscript and subscript of the operator at the same place as in \displaystyle:
\documentclass{article}
\begin{document}
\[
\sum_{i=1}^{n}
\frac{\frac{cf_{n}}{(1+i)^n}}
{\sum\limits_{i=1}^{n}\frac{cf_n}{(1+i)^n}}
, n_{i}
\]
\end{document}
The following example makes the four math style visible:
① \displaystyle
② \textstyle
③ \scriptstyle
④ \scriptscriptstyle
\documentclass{article}
\usepackage{pifont}
\usepackage{amstext}
\usepackage{color}
\newcommand*{\showms}{%
\mathchoice
{{\scriptscriptstyle\text{\color{red}\ding{172}}}}%
{{\scriptscriptstyle\text{\color{red}\ding{173}}}}%
{{\scriptscriptstyle\text{\color{red}\ding{174}}}}%
{{\scriptscriptstyle\text{\color{red}\ding{175}}}}%
}
\begin{document}
\[
\showms\sum_{\showms i=1}^{\showms n}
\showms\frac{
\showms\frac{\showms cf_{\showms n}}{\showms (1+i)^{\showms n}}
}{
\displaystyle
\showms\sum_{\showms i=1}^{\showms n}
\showms\frac{\showms cf_{\showms n}}{\showms(1+i)^{\showms n}}
}\showms,
n_{\showms i}
\]
\[
\showms\sum_{\showms i=1}^{\showms n}
\showms\frac{
\showms\frac{\showms cf_{\showms n}}{\showms (1+i)^{\showms n}}
}{
\showms\sum\limits_{\showms i=1}^{\showms n}
\showms\frac{\showms cf_{\showms n}}{\showms(1+i)^{\showms n}}
}\showms,
n_{\showms i}
\]
\end{document}
Legend:
① \displaystyle
② \textstyle
③ \scriptstyle
④ \scriptscriptstyle
Best Answer
The sole purpose of using
\sfracis to typeset fractions more compactly than is possible with\frac. Using\dfracin the arguments of\sfracflies in the face of using\sfracto begin with.If you simply must use fractional expressions in the arguments of
\sfrac, do give\sfrac{\frac{dy}{dt}}{\frac{dx}{dt}}a try, i.e., use\frac(or\tfrac) instead of\dfrac. However, just omitting the\sfracwrapper and thus writing\frac{dy}{dt} \big/ \frac{dx}{dt}would appear to be a better alternative.