Spacing lines in mathmode

Question

I need to explain two different elements in two different lines of an equation in math mode. I'm using this piece of code:

\begin{align*}
h(z)=0 &\Leftrightarrow \sinh\frac{1}{z}=0 \markno{\Leftrightarrow}{According to ...} \frac{2}{z} = 2\pi i n  \\&\marknoup{\Leftrightarrow}{$n$ is whole} z = \frac{i}{\pi n}
\end{align*}

(I'm shortening to make it clearer)

I'm using these macros:

\newcommand\markno[2]{\begin{array}[t]{@{\,}c@{\,}} #1 \\ \downarrow \\ \makebox[0pt]{\scriptsize #2} \end{array}}
\newcommand\marknoup[2]{\begin{array}[b]{@{\,}c@{\,}} \makebox[0pt]{\scriptsize #2}\\ \uparrow \\ #1 \end{array}}

The thing is, that LaTeX automatically spaces the lines, so that the "According two" is above (in height) "n is whole". I'm using two different arrows exactly to avoid that; I want them to overlap in height, in order to save space.

I tried using \vspace, but for some reason it doesn't work well for me.

Answer 1

You can manually adjust the space between the lines in an align environment by adding an optional argument after the line end; e.g. \\[-5mm] instead of just \\. You could also try using \smash (see page 55 of the Not So Short Introduction, or sections 2 & 3 of A complement to \smash, \llap, and \rlap for details).