How to increase number of contour lines in a plot?

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Mahmoud Abbas
Mahmoud Abbas 2022-4-14
评论： Bjorn Gustavsson 2022-4-14
Hello, could you help me make this plot have 20 controur lines and show their respective values on the plot
f = @(x1,x2) (x1-5)^2+(x2-4)^2;
fcontour(f,[0 10 0 10])
colorbar

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回答（2 个）

Steven Lord
Steven Lord 2022-4-14
Ran in:
f = @(x1,x2) (x1-5).^2+(x2-4).^2; % Vectorized the function
h = fcontour(f,[0 10 0 10]); % Let MATLAB choose the number and height of levels
fprintf("There is a contour at level: %g\n", h.LevelList)
There is a contour at level: 10 There is a contour at level: 20 There is a contour at level: 30 There is a contour at level: 40 There is a contour at level: 50 There is a contour at level: 60
figure
h = fcontour(f,[0 10 0 10], 'LevelList', 0:5:50); % I'll choose the levels
fprintf("There is a contour at level: %g\n", h.LevelList)
There is a contour at level: 0 There is a contour at level: 5 There is a contour at level: 10 There is a contour at level: 15 There is a contour at level: 20 There is a contour at level: 25 There is a contour at level: 30 There is a contour at level: 35 There is a contour at level: 40 There is a contour at level: 45 There is a contour at level: 50
  1 个评论
Mahmoud Abbas
Mahmoud Abbas 2022-4-14
Thank you, this works well however i need the number of contour lines to be exactly 20 and the associated values to be shown in the plot. is this possible?

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Bjorn Gustavsson
Bjorn Gustavsson 2022-4-14
If you check the documentation you will find this advice:
fcontour(f,'LevelList',[-1 0 1])
which adapted to your xy-region would be something like:
fcontour(f,[0 10 0 10],'LevelList',[-1 0 1])
HTH
  2 个评论
Mahmoud Abbas
Mahmoud Abbas 2022-4-14
I tried it but it didn't work and it showed me one contour line. I want the code to plot exactly 20 contours over the specified interval and show their values on the plot
Bjorn Gustavsson
Bjorn Gustavsson 2022-4-14
That is a simple for you to achieve as modifying the levels in the "LevelList". I couldn't be bothered to figure out where to put them since you might want the somewhere else, but for 20 levels between two values you could do something like:
minVal = 0.5; % Still cannot be bothered to find out, so you have do decide.
maxVal = 13; % same as above.
LevelList = linspace(minVal,maxVal,20);
fcontour(f,[0 10 0 10],'LevelList',LevelList)

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