What information is conveyed by the different colors in Matlab's contourf( ) data plots?

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Noob 2020-9-24

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https://ww2.mathworks.cn/matlabcentral/answers/599314-what-information-is-conveyed-by-the-different-colors-in-matlab-s-contourf-data-plots

编辑： Abdolkarim Mohammadi 2020-9-24

采纳的回答： Abdolkarim Mohammadi

在 MATLAB Online 中打开

Hi,

Matlab has a contourf( ) function, which I used a little bit last night to plot the level sets of say,

Z = f(x,y) = x*cos(y)

I called the contour function using one of Mathworks examples, so I used

contourf(X,Y,Z,10)
axis equal

on an evenly-spaced x-y meshgrid.

What do the various colors represent in the contourf( ) plot?

There's no labeling, like, say, a colormap would provide.

My motivation to plot a function's level sets is to then overlay it with plots of convergent sequences xn (maybe with an "x" marker), converging to roots of the function (using some simple methods like gradient-descent and Newton's method that I've been playing with). Namely, I notice that two algorithms may converge to different roots, when starting from the same initial guess -- so I think it would be interesting to visualize this difference and get better intuition for the geometric aspects of various root-finding algorithms.

Thanks,

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Answer 1

Abdolkarim Mohammadi 2020-9-24

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https://ww2.mathworks.cn/matlabcentral/answers/599314-what-information-is-conveyed-by-the-different-colors-in-matlab-s-contourf-data-plots#answer_499975

编辑：Abdolkarim Mohammadi 2020-9-24

在 MATLAB Online 中打开

You can turn on the ShowText property of the contour, or add the color bar:

x = linspace (-5, 5, 51);
y = linspace (-5, 5, 51);
[X,Y] = meshgrid (x, y);
Z = X .* cos(Y);
contourf (X, Y, Z, 'ShowText', 'on');
colorbar ();
axis ('equal'); 