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I have some quantity varying with time (horizontal axis of the plot): it first oscillates then it has a jump (larger than the amplitude of the oscillations), then it continues oscillating. I have that quantity for a discrete set of cases (vertical axis of the plot).

I would like to find an option for ListDensityPlot that would allow me to really emphasize that jump: I don't want a nice smooth color scheme but rather one that would make the small oscillations invisible and would focus on the larger jump.

I can I control ListDensityPlot to do that ?

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(List)DensityPlot is for a two-variable function such as $f(x,y)$, but from your description I understood that you have a single quantity varying in a single variable (time), i.e. $f(t)$. Can you clarify? I thought you had something like Plot[Table[Sin[x] + 3 UnitStep[x - 20] + i, {i, 0, 10, 2}] // Evaluate, {x, 0, 40}]. –  Szabolcs Jul 24 '12 at 10:19
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It would be best if you could give an example, or maybe sample data (with as much information about the location of the jump as possible). –  Szabolcs Jul 24 '12 at 10:21
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2 Answers

up vote 6 down vote accepted

Sample data

pw = Piecewise[{{Sin[5 x + y], x < 5}, {3 + Sin[5 x + y], x > 5}}];

tab = Table[pw, {y, 0, 10, 0.1}, {x, 0, 10, 0.1}];

Expansion function

expand[c_ /; c == 0] = # &;
expand[c_] := 1/2 - ArcTan[c - 2 c #] / ArcTan[c] / 2 &

expand[x] generates a function with expansion factor x.

Table[
  Plot[expand[c][x], {x, 0, 1}],
  {c, 0, 10, 2}
] ~Partition~ 3 // Grid

Mathematica graphics

With expansion

We can use this on the data passed to the ColorFunction like this:

ListDensityPlot[tab, ColorFunction -> (ColorData["SunsetColors"] @ expand[10][#] &)]

Mathematica graphics

Without expansion

The same plot without expansion:

ListDensityPlot[tab, ColorFunction -> ColorData["SunsetColors"]]

Mathematica graphics

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InterpolationOrder?

data = Table[
   With[{r = RandomReal[{0, 5}], 
     t = RandomReal[{0, 2 Pi}]}, {r Cos[t], r Sin[t], 
     Sin[r^2]/r^2}], {10^4}];


ListDensityPlot[data, Mesh \[Rule] None, InterpolationOrder -> 0]

Mathematica graphics

versus

ListDensityPlot[data, Mesh -> None, InterpolationOrder -> Automatic]

Mathematica graphics

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