How to plot the maximum regions given several functions in a 2D plot?

Question

EllaD 2023-7-21

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1998928-how-to-plot-the-maximum-regions-given-several-functions-in-a-2d-plot

评论： EllaD 2023-7-21

I have three functions A(i,j), B(i,j), and C(i,j) which are functions of i and j , where a<i<b and a<j<b.

I want to distinguish and plot regions where each of these functions has the maximum value. Can someone please help me get started?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2023-7-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1998928-how-to-plot-the-maximum-regions-given-several-functions-in-a-2d-plot#answer_1276583

在 MATLAB Online 中打开

idx = max(cat(3, A, B, C), [], 3);
cmap = [.3 0 0;    %light red
        0  .5 0;   %light green
        0 0 .8];   %blue
pcolor(idx); colormap(cmap)
xlabel('i'); ylabel('j')
fake(1) = plot(nan, nan, 'DisplayName', 'A', 'Color', cmap(1));
fake(2) = plot(nan, nan, 'DisplayName', 'B', 'Color', cmap(2));
fake(3) = plot(nan, nan, 'DisplayName', 'C', 'Color', cmap(3));
legend(fake)

10 个评论
显示 8更早的评论隐藏 8更早的评论

Walter Roberson 2023-7-21

pcolor() creates a surface plot internally.

If you were to create an automatic legend for a surface plot, there would be exactly one legend entry for the entire surface plot. We want to created one legend entry for each of the functions we are dealing with.

MATLAB has no direct way of saying, "Add additional legend entries with these properties."

So, instead we use a combination of tricks:

We create one extra graphics object for each legend entry we wish to add
We pass only the handles for those exttra graphics objects to legend(). When you pass legend() a series of graphics objects, it will create legend entries only for the handles you pass in -- in particular in this case, it would not create a legend entry for the surface created by pcolor, just for the plot handles stored in the fake vector
We give Nan coordinates for the extra graphics objects that we are creating just for the purpose of creating legend entries. Graphics objects such as lines and surfaces are only visible if they have some finite coordinates (and in some cases at least multiple adjacent finite coordinates.) You could use inf or -inf for the coordinates instead of NaN, but NaN tends to be used as a matter of informal convention (using NaN instead of -inf or inf makes it easier to do some calculations on the data.)
We do not simply use graphics objects with regular finite coordinates but set Visible off for them, because the finite coordinates can influence what MATLAB picks for the tick positions and how much data is to be visible; non-finite coordinates are ignored for the purpose of calculating such things

So we plot() NaN to create invisible graphics objects that do not disturb other graphics properties, and we do that because the invisible graphics objects still get legend entries.

Bruno Luong 2023-7-21

在 MATLAB Online 中打开

It is still not clear to me how pcolor graphical result has 3 colors, and not more as I assume it takes the average.

A=rand(5);

B=rand(5);

C=rand(5);

[~,idx] = max(cat(3, A, B, C), [], 3)

idx = 5×5

3 2 3 2 1 2 3 2 1 1 2 3 3 1 3 1 2 3 1 1 1 1 2 3 2

idx3 = cat(3,idx(1:end-1,1:end-1), ...

idx(1:end-1,2:end), ...

idx(2:end,2:end), ...

idx(2:end,1:end-1));

mean(idx3,3)

ans = 4×4

2.5000 2.5000 2.0000 1.2500 2.5000 2.7500 1.7500 1.5000 2.0000 2.7500 2.0000 1.5000 1.2500 2.0000 2.2500 1.7500

min(idx3,[],3)

ans = 4×4

2 2 1 1 2 2 1 1 1 2 1 1 1 1 1 1

max(idx3,[],3)

ans = 4×4

3 3 3 2 3 3 3 3 3 3 3 3 2 3 3 3

pcolor(idx);

It must have some odd algorithm to decide the color.

But never mind I rarely (never) use pcolor.

EllaD 2023-7-21

Thank you all for the feedback on pcolor. Appreciate it. :)

请先登录，再进行评论。

How to plot the maximum regions given several functions in a 2D plot?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

10 个评论
显示 8更早的评论隐藏 8更早的评论

更多回答（0 个）

另请参阅

类别

标签

Community Treasure Hunt

How to plot the maximum regions given several functions in a 2D plot?

0 个评论 显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

10 个评论 显示 8更早的评论隐藏 8更早的评论

更多回答（0 个）

另请参阅

类别

标签

Community Treasure Hunt

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

10 个评论
显示 8更早的评论隐藏 8更早的评论