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I'm trying to make a plot that has a lower half of the y-axis going from 0 to 0.9 and an upper half that goes from 0.9 to 1.0. So that this second interval is zoomed. I've tried to do this with piecewise scaling functions without success. And I can't think of a solution that doesn't involve creating two different plots and combine them in a graphics column with no spacing (would want to avoid this since this plot is included in one bigger set of plots and this would ruin the alignment I already achieved).

It would be something like the image. Thank you in advance!

Related: How to break the x axis of a plot?

enter image description here

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  • $\begingroup$ Hi Bill, actually the line was just a simplification, the function I want to plot is not a line. $\endgroup$
    – kl0z
    Nov 23, 2020 at 11:55

1 Answer 1

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You can use the option ScalingFunctions! They're easy to use but a bit tricky to understand. I'll be honest: I don't know what the second function it asks for does, but the documentation says to use the inverse function of the first one, so that's what I'll do. I'd love for someone to explain it.

So, I used a piecewise function that sends the interval $[0,0.9]$ to $[0,0.5]$ linearly, and sends $[0.9,1]$ to $[0.5,1]$ linearly. If you're rusty on how to do this, just look up point-slope form or any other method of graphing a line given two points on the line.

Note the explicit specification of Ticks to create the ticks at 0, 0.9, and 1 on the y-axis.

ListPlot[Table[x, {x, 0, 1, 0.01}],
    Joined -> True, DataRange -> {0, 1}, PlotRange -> {0, 1}, 
    ScalingFunctions ->
        {Piecewise[{{0.5 #/0.9, # <= 0.9}, {(0.5/0.1) (# - 0.9) + 0.5, # > 0.9}}] &, 
         (*The next element in the list is just InverseFunction surrounding the above function: *)
         InverseFunction[Piecewise[{{0.5 #/0.9, # <= 0.9}, {(0.5/0.1) (# - 0.9) + 0.5, # > 0.9}}] &]},
    Ticks -> {Automatic, {0, 0.9, 1}}]

A plot where the bottom half of the y-axis goes from 0 to 0.9 and the top half goes from 0.9 to 1.

You could also use your above solution of making two separate graphs, but you'd need to combine them with Show, play with the ticks by giving each of them explicit labels that differed from their "actual" values, and use PlotRange to expand the x-axis of the first one (which determines the overall settings) to include the domain of the second one. To my taste, it's more complicated and ad-hoc, but doable, and perhaps preferable depending on what you're comfortable with!

EDIT: About the second list element in ScalingFunctions: from searching SE, it seems to be the case that inverse functions are simply hard to compute, so it asks the user if they have an optimized one that it can use. I'm not sure exactly which parts of the graph are affected, though, as changing it seems to produce no visible difference here.

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    $\begingroup$ The inverse scaling function is used to reconstruct the tick labels on the scaled axis. The problem is the inverse scaling function is not always InverseFunction[scaling_function] and sometimes some points might not be well defined or the inverse values are not unique; so the design solution is to leave it to the users to define it, should it come to the situations described previously. Related article is in the doc tutorial/MathematicalFunctions#21968. $\endgroup$ Dec 19, 2020 at 4:20

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