Skip to main content

Plotting piecewise functions with distinct colors - issue found



I've been making use of the following thread: Plotting piecewise function with distinct colors in each section


A handy feature I found there goes as follows:


Module[{i = 1},
Plot[pw, {x, -2, 2}, PlotStyle -> Thick]
/. x_Line :> {ColorData[1][i++], x}
]


pw is some piecewise function, and this code makes every region defined in pw to have a different color in the plot. However, this only seems to work when Plot "detects" a discontinuity in the line object it is drawing. I know this because specifying Exclusions->None leaves only 1 color, and changing PlotPoints also affects coloring.


I suppose I could abandon that method and try the other ones in the thread I linked, but the syntax they use is beyond my current knowledge. Although that's something I can overcome, those other methods also seem like too much work for something that I feel should be simple to implement.


Basically, I'm looking for the best way to do this piecewise coloring in Plot with the smallest amount of code.


Edit: Any piecewise function with Exclusions->None will replicate this. For the sake of an example, I will paste the function I've been wrestling with. It's very long and messy, but I believe that level of precision is necessary to reproduce the problem:


ux[x_] = Piecewise[{{7.947574298019541*^6 + x*(0.030685326533756174 - 2.1557891405527275*^-11*x - 1.1279177212121211*^-18*x^2) - 507272.5381818181*Log[6.371*^6 + 1.*x], 
0 <= x <= 7157200}, {8.0095531822173735*^6 + x*(0.022025671333701383 - 2.1557891405527275*^-11*x - 1.1279177212121211*^-18*x^2) - 507272.5381818181*Log[6.371*^6 + 1.*x],
7157200 <= x <= 14314400}, {8.053211120764352*^6 + x*(0.018975739897736304 - 2.1557891405527275*^-11*x - 1.1279177212121211*^-18*x^2) - 507272.5381818181*Log[6.371*^6 + 1.*x],
14314400 <= x <= 21471600}, {8.073469465513253*^6 + x*(0.0180322450138478 - 2.1557891405527275*^-11*x - 1.1279177212121211*^-18*x^2) - 507272.5381818181*Log[6.371*^6 + 1.*x],
21471600 <= x <= 28628800}, {8.07699092547415*^6 + x*(0.017909240907462088 - 2.1557891405527275*^-11*x - 1.1279177212121211*^-18*x^2) - 507272.53818181815*Log[6.371*^6 + 1.*x],

28628800 <= x <= 35786000}}, 0];
Module[{i = 1}, plt5 = Plot[ux[x], {x, 0, 35786000}] /. x_Line :> {ColorData[100][i++], x}]

enter image description here



Answer



Just to put Pickett's answer in here officially,


ux = Piecewise[{{7.947574298019541*^6 + # (0.030685326533756174 - 
2.1557891405527275*^-11 # - 1.1279177212121211*^-18 #^2) -
507272.5381818181*Log[6.371*^6 + 1. #],
0 <= # <=

7157200}, {8.0095531822173735*^6 + # (0.022025671333701383 -
2.1557891405527275*^-11 # - 1.1279177212121211*^-18 #^2) -
507272.5381818181*Log[6.371*^6 + 1. #],
7157200 <= # <=
14314400}, {8.053211120764352*^6 + # (0.018975739897736304 -
2.1557891405527275*^-11 # - 1.1279177212121211*^-18 #^2) -
507272.5381818181*Log[6.371*^6 + 1. #],
14314400 <= # <=
21471600}, {8.073469465513253*^6 + # (0.0180322450138478 -
2.1557891405527275*^-11 # - 1.1279177212121211*^-18 #^2) -

507272.5381818181*Log[6.371*^6 + 1. #],
21471600 <= # <=
28628800}, {8.07699092547415*^6 + # (0.017909240907462088 -
2.1557891405527275*^-11 # - 1.1279177212121211*^-18 #^2) -
507272.53818181815*Log[6.371*^6 + 1. #],
28628800 <= # <= 35786000}}, 0] &;

The point here is to break the plot up into different Line objects using Exclusions. We get the exclusions from the function (which only works if the function is a pure function)


exclusions = ux[[1, 1, All, 2, 1]]
(* {0, 7157200, 14314400, 21471600, 28628800} *)



Module[{i = 1},
plt5 = Plot[ux[x], {x, 0, 35786000}, Exclusions -> exclusions] /.
x_Line :> {ColorData[100][i++], x}]

enter image description here


I had gone through the process of making a piecewise ColorFunction for this, only to find that the second answer in the linked post, by David, does it more elegantly, so I'll just reiterate it here.


colorFunction = ux;
colorFunction[[1, 1, All, 1]] =

ColorData[100][#] & /@ Range@Length@colorFunction[[1, 1]];

Plot[ux[x], {x, 0, 35786000}, ColorFunction -> colorFunction,
ColorFunctionScaling -> False]

enter image description here


If anyone can tell why that looks so much worse I would be grateful.


Comments

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...

How to thread a list

I have data in format data = {{a1, a2}, {b1, b2}, {c1, c2}, {d1, d2}} Tableform: I want to thread it to : tdata = {{{a1, b1}, {a2, b2}}, {{a1, c1}, {a2, c2}}, {{a1, d1}, {a2, d2}}} Tableform: And I would like to do better then pseudofunction[n_] := Transpose[{data2[[1]], data2[[n]]}]; SetAttributes[pseudofunction, Listable]; Range[2, 4] // pseudofunction Here is my benchmark data, where data3 is normal sample of real data. data3 = Drop[ExcelWorkBook[[Column1 ;; Column4]], None, 1]; data2 = {a #, b #, c #, d #} & /@ Range[1, 10^5]; data = RandomReal[{0, 1}, {10^6, 4}]; Here is my benchmark code kptnw[list_] := Transpose[{Table[First@#, {Length@# - 1}], Rest@#}, {3, 1, 2}] &@list kptnw2[list_] := Transpose[{ConstantArray[First@#, Length@# - 1], Rest@#}, {3, 1, 2}] &@list OleksandrR[list_] := Flatten[Outer[List, List@First[list], Rest[list], 1], {{2}, {1, 4}}] paradox2[list_] := Partition[Riffle[list[[1]], #], 2] & /@ Drop[list, 1] RM[list_] := FoldList[Transpose[{First@li...

front end - keyboard shortcut to invoke Insert new matrix

I frequently need to type in some matrices, and the menu command Insert > Table/Matrix > New... allows matrices with lines drawn between columns and rows, which is very helpful. I would like to make a keyboard shortcut for it, but cannot find the relevant frontend token command (4209405) for it. Since the FullForm[] and InputForm[] of matrices with lines drawn between rows and columns is the same as those without lines, it's hard to do this via 3rd party system-wide text expanders (e.g. autohotkey or atext on mac). How does one assign a keyboard shortcut for the menu item Insert > Table/Matrix > New... , preferably using only mathematica? Thanks! Answer In the MenuSetup.tr (for linux located in the $InstallationDirectory/SystemFiles/FrontEnd/TextResources/X/ directory), I changed the line MenuItem["&New...", "CreateGridBoxDialog"] to read MenuItem["&New...", "CreateGridBoxDialog", MenuKey["m", Modifiers-...