# Fading curves based on a function?

Posted 9 months ago
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 I have some code that outputs what I want, although I may change the function later. However, I want the output to be like a screenshot I have provided, such that it fades as with the properties of another function.Here is the code: ClearAll["Global*"]; xi = 2; k0 = 9; Print["k0=", k0, " xi=", xi]; \ Show[Table[ sol = NDSolve[{D[xtraj[t], t] == (Sinh[ xtraj[t] (t - xi)])/((Cos[xtraj[t]]) + (Cosh[ xtraj[t] (t - xi)])), xtraj[0] == n}, xtraj[t], {t, 0, 4}]; ParametricPlot[{t, xtraj[t]} /. sol, {t, 0, 4}, PlotRange -> All, PlotStyle -> {Blue, Full, Medium}, AxesStyle -> Thickness[.003], LabelStyle -> {Black, Medium}, AxesLabel -> {xtraj, t}], {n, -4, 4 - 0.5, 0.5}]] Here is the output - or a simplified version of it:And now this is what I would like - the fading is based upon another function - given below. Here is the fading function: (E^(-2 (-2 + t + x)^2) Sqrt[2 \[Pi]] (1 + E^(8 (-2 + t) x) + 2 E^(4 (-2 + t) x) Cos[10 x])) It is a tricky one that I really would like to solve.
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Posted 9 months ago
 Have you tried ColorFunction and ColorFunctionScaling? For example xi = 2; k0 = 9; Show[ Table[sol = NDSolve[{D[xtraj[t], t] == (Sinh[ xtraj[t] (t - xi)])/((Cos[xtraj[t]]) + (Cosh[ xtraj[t] (t - xi)])), xtraj[0] == n}, xtraj[t], {t, 0, 4}]; ParametricPlot[{t, xtraj[t]} /. sol, {t, 0, 4}, PlotRange -> All, ColorFunction -> Function[{x, y}, Directive[Opacity[Abs[y]/4], Blue]], ColorFunctionScaling -> False], {n, -4, 4 - 0.5, 0.5}]] 
Posted 9 months ago
 Gianluca, this is a color function on y, if you look closely at my second diagram you will see that the fade is the same along each curve, whereas this code fades in the direction of y evenly.
Posted 9 months ago
 Mine was just a hint in a general direction. I leave it to you to fine-tune it.
Posted 9 months ago
 I understand but to make the function fade this will not work, I've already tried it but thanks.
 This may be closer to what you want: xi = 2; k0 = 9; fadingFunction[t_, x_] = (E^(-2 (-2 + t + x)^2) Sqrt[ 2 \[Pi]] (1 + E^(8 (-2 + t) x) + 2 E^(4 (-2 + t) x) Cos[10 x])); sol = ParametricNDSolveValue[{D[xtraj[t], t] == (Sinh[ xtraj[t] (t - xi)])/((Cos[xtraj[t]]) + (Cosh[ xtraj[t] (t - xi)])), xtraj[0] == n}, xtraj, {t, 0, 4}, {n}]; Plot[Table[sol[n][t], {n, -4, 4 - 0.5, 0.5}], {t, 0, 4}, PlotRange -> All, ColorFunction -> Function[{t, x}, Blend[{Blue, White}, Rescale[ArcTan[fadingFunction[t, x]], {0, Pi/2}]]], ColorFunctionScaling -> False] `