Spacing of contours in BarLegend (Ver. 10 vs 11)

Question

I recently started using Version 11, and I encountered the following problem. I use this code to make a contour plot:

myfunct[x_, y_] := 1.64 Exp[-6 (x^3 + y)] + 0.02 Sin[8 x + y] + 0.02;
ContourPlot[
  myfunct[x,y], {x, 0, 1}, {y, 0, 1},
  PlotRange -> Full,
  Contours -> Table[x^2, {x, 0, Sqrt[1.7], 0.05}],
  ContourStyle -> Thin,
  FrameStyle -> Directive[FontFamily -> "Arial", 18, Black],
  PlotLegends -> BarLegend[
    Automatic,
    LabelStyle -> Directive[FontFamily -> "Arial", FontSize -> 18, Black],
    LegendMarkerSize -> 250
  ],
  ImageSize -> 400,
  MaxRecursion -> 4
]

And here is the comparison between the two versions (I can't disclose the plotted function, but the one given in the code above has a similar behaviour):

The behaviour I'm interested in is the one from Version 10. The legend does not scale, neither do the ticks (0, 0.5, 1.0, 1.5), the contours however scale according to the positions I have chosen for them.

My question is how to force Mathematica 11 to use the old style? Is there possibly an undocumented option that can do it?

Answer 1

I can reproduce the behavior you report but I don't think it's a bug. I think it's an improvement. Why? Because, in V11, you are getting a more accurate bar legend. The contour marks and labels are at values taken from actual contours in the plot. In V10, they were an interpolation of the contour values.

myfunct[x_, y_] := 1.64 Exp[-6 (x^3 + y)] + 0.02 Sin[8 x + y] + 0.02

ContourPlot[myfunct[x, y], {x, 0, 1}, {y, 0, 1},
  PlotRange -> Full,
  Contours -> Table[x^2, {x, 0, Sqrt[1.7], 0.05}], 
  FrameStyle -> Directive[FontFamily -> "Arial", 18, Black], 
  PlotLegends -> 
    BarLegend[Automatic, 
      LabelStyle -> 
        Directive[
          FontFamily -> "Arial", FontSize -> 18, Black], LegendMarkerSize -> 250], 
  ImageSize -> 400,
  MaxRecursion -> 4]

You specified the contours with

Table[x^2, {x, 0, Sqrt[1.7], 0.05}]

{0., 0.0025, 0.01, 0.0225, 0.04, 0.0625, 0.09, 0.1225, 0.16, 0.2025, 0.25, 0.3025, 0.36, 0.4225, 0.49, 0.5625, 0.64, 0.7225, 0.81, 0.9025, 1., 1.1025, 1.21, 1.3225, 1.44, 1.5625, 1.69}

Note that all the bar chart labels values appear in the above list, which means you are getting a much more accurate bar legend than you got in V10.

Answer 2

I managed to get the old behaviour by just adding two lines to the code:

myfunct[x_, y_] := 1.64 Exp[-6 (x^3 + y)] + 0.02 Sin[8 x + y] + 0.02;

ContourPlot[
  myfunct[x, y], {x, 0, 1}, {y, 0, 1},
  PlotRange -> Full,
  Contours -> Table[x^2, {x, 0, Sqrt[1.7], 0.05}],
  ContourStyle -> Thin,
  FrameStyle -> Directive[FontFamily -> "Arial", 18, Black], 
  PlotLegends -> BarLegend[
    Automatic, None, (* added due to MinHsuanPeng *)
    LabelStyle -> 
    Directive[FontFamily -> "Arial", FontSize -> 18, Black],
    LegendMarkerSize -> 250,
    "StyledContours" -> Table[{x^2, Opacity[0.5]}, {x, 0, Sqrt[1.7], 0.05}] (* added *)
  ],
  ImageSize -> 400,
  MaxRecursion -> 4
]

And the output is basically identical to the Ver. 10 plot: