#2887 zooming in multiplots with logscaled and linked axes fails

[Anonymous]

I've got a multiplot with linked x and x2 axes, and a logscaled y - axis, and the new multiplot zoom feature in 6.0pl5 fails, seemingly because it thinks the same axis is linked and logscaled.

Here's a minimal example:

set multi layout 1,2
plot x
set logsc y
set link x2 via x*2 inverse x/2
set x2tics
plot exp(x)
unset multi
# now try to zoom with the mouse in one of the graphs

gives

gnuplot> must unlink axis before setting it to nonlinear

I notice that also the x and x2 coordinate display in the terminal status line only shows nan when a graph with logsc y and linked x axes is plotted in multiplot mode.

set multi
set logsc y
set link x2 via x inverse x
set x2tics
plot x
# x coordinates are only shown as "nan" in the interactive terminal

So the problem occurs before the attempt to zoom, apparently. It works if the links doesn't do any math, i.e. if you leave out the via ... inverse ... specifiers.

[Ethan Merritt]

Showing NaN rather than a coordinate for the secondary axis of a linked pair or nonlinear mapping is an intrinsic limitation of the design. The underlying problem is that the forward and reverse mapping functions must be evaluated by the program core, but during mousing the display window does not necessarily share any context (variables, functions, etc) with the core code.

But the error, and the lack of mouse tracking for x, are both bugs.
Now fixed in 6.1 and queued for 6.0