Skip to main content

How can I combine two color schemes for plotting?


I want to use ListContourPlot to display all negative values using one colorscheme and all positive values using another color scheme. This question Define a color function using Piecewise gives some hints, but if I use something like this


colorFunc[x_] := Piecewise[{{"AlpineColors", x >= 0},
{"SouthwestColors", x < 0}}];


ListContourPlot[data, ColorFunction -> colorFunc]

I get the error message:



AlpineColors is not a Graphics primitive or directive



Any idea?


Thanks in advance.


Edit1: I used kguler's suggestion which works with most data. However, in some cases I get results like this: enter image description here


using



ListContourPlot[data, Contours -> 10,ColorFunction -> (Piecewise[{{ColorData["NeonColors"][#], # > 0.5}, {ColorData["Aquamarine"][#], # <= 0.5}}] &),ContourLabels -> All]

The Aquamarine colors should code only for negative values and not for positive ones. What does go wrong?



Answer



You can do


ListContourPlot[Table[Sin[i + j^2], {i, 0, 3, 0.1}, {j, 0, 3, 0.1}], 
 ColorFunction -> (Piecewise[{{ColorData["AlpineColors"][#], # >= .5}, 
                              {ColorData["SouthwestColors"][#], # < .5}}] &)]

enter image description here



Update: Rescaling the range of the function ColorData[_scheme_]using the form ColorData[{_scheme_, {min, max}}] together with the option ColorFunctionScaling->False gives more control:


dt = Table[Sin[i + j^2], {i, 0, 3, 0.1}, {j, 0, 3, 0.1}];
{min, max} = Through@{Min, Max}@dt;
ListContourPlot[dt, ColorFunctionScaling -> False,
 ColorFunction -> (Piecewise[{{ColorData[{"AlpineColors", {min, max}}][#], # >= 0},
            {ColorData[{"SouthwestColors", {min, max}}][#], # < 0}}] &)]
(* same picture *)

Update 2: Dealing with the issue mention in the comments:


In version 9



dt = Table[Sin[i + j^2], {i, 0, 3, 0.1}, {j, 0, 3, 0.1}]; dt[[10, 10]] = -0.01;
{min, max} = Through@{Min, Max}@dt;
ListContourPlot[dt, ColorFunctionScaling -> False,
 ContourLabels -> True, MaxPlotPoints -> 500,
 ColorFunction -> (Piecewise[{{ColorData[{"AlpineColors", {min, max}}][#], # >= 0},
      {ColorData[{"SouthwestColors", {min, max}}][#], # < 0}}] &)]

gives


enter image description here


Using the option InterpolationOrder->0 I get: enter image description here



Zooming in around dt[[10,10]] using PlotRange -> {{9.75, 10.25}, {9.75, 10.25}}, I get


enter image description here


Comments

Post a Comment

Popular posts from this blog

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...
Post a Comment
Read more

mathematical optimization - Minimizing using indices, error: Part::pkspec1: The expression cannot be used as a part specification

I want to use Minimize where the variables to minimize are indices pointing into an array. Here a MWE that hopefully shows what my problem is. vars = u@# & /@ Range[3]; cons = Flatten@ { Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; Minimize[{Total@((vec1[[#]] - vec2[[u[#]]])^2 & /@ Range[1, 3]), cons}, vars, Integers] The error I get: Part::pkspec1: The expression u[1] cannot be used as a part specification. >> Answer Ok, it seems that one can get around Mathematica trying to evaluate vec2[[u[1]]] too early by using the function Indexed[vec2,u[1]] . The working MWE would then look like the following: vars = u@# & /@ Range[3]; cons = Flatten@{ Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; NMinimize[ {Total@((vec1[[#]] - Indexed[vec2, u[#]])^2 & /@ R...
Post a Comment
Read more

plotting - Plot 4D data with color as 4th dimension

I have a list of 4D data (x position, y position, amplitude, wavelength). I want to plot x, y, and amplitude on a 3D plot and have the color of the points correspond to the wavelength. I have seen many examples using functions to define color but my wavelength cannot be expressed by an analytic function. Is there a simple way to do this? Answer Here a another possible way to visualize 4D data: data = Flatten[Table[{x, y, x^2 + y^2, Sin[x - y]}, {x, -Pi, Pi,Pi/10}, {y,-Pi,Pi, Pi/10}], 1]; You can use the function Point along with VertexColors . Now the points are places using the first three elements and the color is determined by the fourth. In this case I used Hue, but you can use whatever you prefer. Graphics3D[ Point[data[[All, 1 ;; 3]], VertexColors -> Hue /@ data[[All, 4]]], Axes -> True, BoxRatios -> {1, 1, 1/GoldenRatio}]
Post a Comment
Read more