The easiest way to understand the meaning of leading is to get a piece of paper and draw two lines. On these two lines, write some text. the distance between these two lines is the leading.
When typesetting the only "constant" parameter for laying out text is the baseline. Descenders, diagritics and subscripts can extend below this line. That is why normally everything relates to the baseline and not the bounding box of the letters.
For a good article and leading definition "woos" see http://www.creativepro.com/article/just-say-no-automatic-leading and of course Knuth did not help much in calling it "baselineskip".
As a general rule increasing the linespacing is bad. (Of course this assumes that the default spacing has been set appropriate to the current font). If the inline math doesn't fit within the specified line spacing consider changing that before changing the global line spacing.
For the examples given
\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator{\Hom}{Hom}
\usepackage{mathpazo}
\showoutput
\showboxdepth5
\begin{document}
\noindent
\parbox{.4\textwidth}{
xx xx xx xx xx xx xx\\
%$\left(\frac{2\pi i}{r}\right)$\\
$(\frac{2\pi i}{r})$\\
xx xx xx xx xx xx xx\\
$\Hom^{(c,d)}$\\
xx xx xx xx xx xx xx
}
\parbox{.4\textwidth}{
xx xx xx xx xx xx xx\\
xx xx xx xx xx xx xx\\
xx xx xx xx xx xx xx\\
xx xx xx xx xx xx xx\\
xx xx xx xx xx xx xx}
\end{document}
using Computer Modern they both fit into the exiting space. Using mathpazo the \Hom example fits but the \left \right construction is too big. Using \left \right in inline math is a bit suspect anyway and if you just use normal size brackets it fits within the specified baseline.
In general you should set your settings for the space that you consider acceptable and then if the math doesn't fit in the space, use display math or a variant notation or something (sometimes you can just use \smash to hide the hight even though it could then overprint a descender on the line above, if you know there is no descender then...) Here for example is your passage unchanged on the original baselineskip set by the font package, but with superscripts made smaller. \lineskip glue is not used, only \baselineskip glue as shown in the log, so confirming that baseline spacing has been preserved. There are alternatives such as playing with the font dimen parameters that control script positions. But I ended up not using that, so commented out.
\documentclass[12pt]{article}
\usepackage{amsmath}
\DeclareMathOperator{\Hilb}{Hilb}
\DeclareMathOperator{\Hom}{Hom}
\newcommand{\C}{\mathbb{C}}
\showoutput
\showboxdepth4
\usepackage{mathpazo}
\DeclareMathSizes{12pt}{12}{6.5}{5}
\begin{document}
\sbox0{$aaa$}
\typeout{
13 \the\fontdimen13\textfont2^^J
14 \the\fontdimen14\textfont2^^J
15 \the\fontdimen15\textfont2^^J
16 \the\fontdimen16\textfont2^^J
17 \the\fontdimen17\textfont2^^J
18 \the\fontdimen18\textfont2^^J
19 \the\fontdimen19\textfont2^^J
19 \the\fontdimen8\textfont3^^J
}
%
% \fontdimen13\textfont2=\dimexpr(\fontdimen13\textfont2)/10\relax
% \fontdimen14\textfont2=\dimexpr(\fontdimen14\textfont2)/10\relax
% \fontdimen15\textfont2=\dimexpr(\fontdimen15\textfont2)/10\relax
% \fontdimen16\textfont2=\dimexpr(\fontdimen16\textfont2)/10\relax
% \fontdimen17\textfont2=\dimexpr(\fontdimen17\textfont2)/10\relax
% \fontdimen18\textfont2=\dimexpr(\fontdimen18\textfont2)/10\relax
% \fontdimen19\textfont2=\dimexpr(\fontdimen19\textfont2)/10\relax
% \fontdimen8\textfont3=\dimexpr(\fontdimen8\textfont3)/10\relax
The case $\Hilb^G_G$ where $v=G$ is the regular representation of $G$ has been studied
in particular depth, and is frequently referred to as GHilb. Since the ideal sheaf of
a generic point on $[\C^2/G]$ corresponds to the regular representation of $G$, the
Hilbert-Chow morphism $\Hilb^G_G\to\C^2/G$ is an isomorphism away from $0$. Since
$\Hilb^G_G$ is smooth, this is a resolution of singularities. In fact, it turns out
that it is the minimal resolution of $\C^2/G$, and has been much studied.
The action of $(\C^*)^2$ on $\C^2$ induces an action on $\Hilb_n(\C^2)$, and since if
$G\subset (\C^*)^2$ then in particular $G$ and $(\C^*)$ commute, we also have a
$(\C^*)^2$ action on $\Hilb_G(\C^2)$. The fixed points of this action on
$\Hilb_n(\C^2)$ are precisely the monomial ideas. Since $G\subset (\C^*)^2$, we see
that the monomial ideals are also the fixed points of the action on $\Hilb_n(\C^2)^G$.
The space of $\Hom^{(c,d)}_\C(\mathcal{I},R/\mathcal{I})$ of weight $(c,d)$ vector
space maps corresponds to the cells in $\lambda$ and above $P_\lambda(c,d)$, while the
space $\Hom^{(c,d)}_R (\mathcal{I},R/\mathcal{I})$ of weight $(c,d)$ maps of $R$-
modules corresponds to the bounded regions below $P_\lambda$ and above
$P_\lambda(c,d)$.
\end{document}
Best Answer
You should set the parameter
\lineskiplimitto a negative value to avoid the lines from spreading. This behavior is explained in the TeXbook pg.78.The TeX engine adds more space between the lines if their separation is smaller than
\lineskiplimit; therefore setting it to a large negative value has the effect that a correction (which goes under the name\lineskip) is never applied.Therefore simply add
\setlength{\lineskiplimit}{-100pt}to the preamble of your document. All the lines will be equally spaced no matter their content. This is what you want.Taking the MWE from @jfbu that's what the output looks like after setting the lineskiplimit: