Placing math environments inside math environments

Question

I have a macro which appears throughout my document in various places:

\newcommand{\placefraction}[2]{
    $\frac{#1}{#2}$
}

Sometimes it is placed with regular text. Sometimes it is placed within other math modes. However, the document won't compile if it is placed inside another math mode.

None of my math ever appears in displayed formulas, it is always part of the paragraph.

• How can I have a macro which sometimes appears inside math mode, sometimes outside, but itself contains math mode?

Answer 1

Use the \ensuremath macro

\newcommand{\placefraction}[2]{%
    \ensuremath{\frac{#1}{#2}}%
}

The % at the end of the line prevent extra spaces as Boris said in his answer.

---

But I wonder why you want this. In my eyes it’s more consistent to write all math in a math „environment“ (= markup). For example I’ll write

... Assuming that $x=0$ we can see that $\placefraction{1}{2}$ is obviously not
the same as $1+\placefraction{2}{8}-x$ ...

instead of

... Assuming that $x=0$ we can see that \placefraction{1}{2} is obviously not
the same as $1+\placefraction{2}{8}-x$ ...

because x=0, \placefraction{1}{2} and 1+\placefraction{2}{8}-x are from the same kind (math formulas) and should be treated in the same way, which is put both in $…$ in this case.

_{See Ryan’s comment …}

Answer 2

\ensuremath is intended for this purpose. Also, you may want to protect against spurious spaces:

\newcommand{\placefraction}[2]{%
    \ensuremath{\frac{#1}{#2}}%
}