[Tex/LaTex] have a dot and a double subscript at a single letter

Question

I cannot get a double subscript to a letter that has a dot on it.

I only get what is in the first line of the picture, but what I want is the upper left with the dot only on the v. Note that the second vkd is not right.

I use this code

\documentclass[a4paper,10pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\begin{document}

% no errors here\dots
${v_k}_d$
${{\dot{v}}_{k_d}$
${\dot{v_k}_d}$

% this does not work as I thought it should
${{{\dot{v}}_k}}_d$
${{\dot v}_k}_d$
${\dot v_k}_d$

\end{document}

Any ideas??

Follow up

As the comments have shown, there is some doubt that these double subscripts are really necessary. They may be hardly visible, but they flatter the eyes – as I think – and make reading more comfortable. The picture below is what I write in original size.

This is also what the \usepackage{microtype} does. And, kerning doesn't bother you unless you know about it… Cf. this xkzd cartoon.

Answer 1

I find the notation

${v_{k}}_d$

unclear; readers won't be able to distinguish it from

$v_{kd}$

However, if you really insist on doing it that way, you just have to add a pair of braces; I add what I'd do, instead.

\documentclass{article}

\begin{document}

${v_{k}}_{d}$

${{}\dot{v}_{k}}_{d}$

Better:

$(v_{k})_{d}$

$(\dot{v}_{k})_{d}$

\end{document}

It's a problem with math accent that sometimes shows up; in an expression such as ${\dot{v}_k}$ the outer braces are stripped off by rule, because they contain a single Acc atom; therefore the intuitive

${\dot{v}_k}_d$

gives a Double subscript error. Adding an empty subformula avoids the problem.