Positioning with `current axis` depending on limits?

Question

I try to specify the x axis label position below the x axis arrow at the same baseline like the xticklabels. It works fine for most plots. However, when modifying the range of the y axis with ymin=..., the coordinate of current axis.south east changes (which I don't like), but in addition, the position of the coordinate changes towards an unexpected direction.

What is the reason that truncated plots result in a strangely modified current axis environment?

In the following, pictures with ymin=1.0 (ok), ymin=0.8 (ok), ymin=1.2 (undesirable result), and ymin not defined (strange result) are provided, together with an MWE.

MWE:

\documentclass{standalone}
\usepackage{tikz,pgfplots}
\usetikzlibrary{calc}
\pgfplotsset{compat=1.13}
\begin{document}

\begin{tikzpicture}
\begin{axis}[
        axis x line=bottom,
        every axis x label/.style={at={($ (current axis.south east) + (0,-2.135pt)$)},red,anchor=base,yshift=-0.75em},
        xticklabel style={anchor=base,yshift=-0.75em},
        xlabel={$t$}, 
        ymin=1.0, % <-- min of addplot
        %ymin=1.2, % <-- random truncation
    ]
    \addplot[black] coordinates {(0,2) (1,1) (2.2,2)};

\end{axis}
\end{tikzpicture}
\end{document}

Answer 1

You can use the xticklabel cs to position the x axis label:

every axis x label/.style={at={(xticklabel cs:1)},anchor=south,red},
typeset ticklabels with strut,
xlabel={$t$\strut},

The \strut inside xlabel and option typeset ticklabels with strut are used to ensure that the ticklabels and the label have the same height and the same depth.

Code:

\documentclass[tikz,margin=5pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.13}
\begin{document}
\foreach \ymin in {.8,1,1.2}{
\begin{tikzpicture}
\begin{axis}[
        axis x line=bottom,
        every axis x label/.style={at={(xticklabel cs:1)},anchor=south,red},
        typeset ticklabels with strut,
        xlabel={$t$\strut}, 
        ymin=\ymin
    ]
    \addplot[black] coordinates {(0,2) (1,1) (2.2,2)};
\end{axis}
\end{tikzpicture}}
\end{document}

---

Update:

If you really want to manually shift the x axis label by absolute values like in your example use either

at={([yshift=-2.135pt]current axis.south east)}

or

at={($ (current axis.south east) + (0pt,-2.135pt)$)}

Note, that you have to use 0pt instead only 0.

Code:

\documentclass[margin=5pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.13}
\usetikzlibrary{calc}
\begin{document}
\foreach \ymin in {.8,1,1.2}{
\begin{tikzpicture}
\begin{axis}[
        axis x line=bottom,
        every axis x label/.style={
            at={($ (current axis.south east) + (0pt,-2.135pt)$)},
            red,anchor=base,yshift=-0.75em
        },
        xticklabel style={anchor=base,yshift=-0.75em},
        xlabel={$tg$}, 
        ymin=\ymin
    ]
    \addplot[black] coordinates {(0,2) (1,1) (2.2,2)};
\end{axis}
\end{tikzpicture}}
\end{document}