I want to change the color of the markers in scatter plot which are below the function line

Question

Haseeb Hashim 2022-4-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1693650-i-want-to-change-the-color-of-the-markers-in-scatter-plot-which-are-below-the-function-line

评论： Star Strider 2022-4-11

I have the following code

clc
clear
close all
d = 4;
N = 1000;
X = linspace(0,d,N);
func = @(X) 2*X.*cos(X.^2).*exp(sin(X.^2)) + 14;
limit = func(X);
x = 4*rand(1,N);
y = 25*rand(1,N);
figure(1),hold on
h = scatter(x,y,10,'markerfacecolor','b');
plot(X,limit,'k-','linew',1.3)
for i = 1:N
    
    if any(y(i) < limit)
        set(h,'YData','MarkerFaceColor','r','Markeredgecolor','r')    
    end
    
end

but it keeps giving the following error

Error using matlab.graphics.chart.primitive.Scatter/set

Invalid parameter/value pair arguments.

Any help would be appreciated

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Walter Roberson 2022-4-11

What is the difference between this and https://www.mathworks.com/matlabcentral/answers/1693635-i-want-to-change-the-color-of-markers-in-scatter-plot-which-are-greater-than-the-specified-values-bu?s_tid=srchtitle ?

Haseeb Hashim 2022-4-11

Sorry I posted it twice But please help me on this do I need to plot in a loop for this or is there are another solution

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Answer 1

Star Strider 2022-4-11

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https://ww2.mathworks.cn/matlabcentral/answers/1693650-i-want-to-change-the-color-of-the-markers-in-scatter-plot-which-are-below-the-function-line#answer_940065

在 MATLAB Online 中打开

d = 4;

N = 1000;

X = linspace(0,d,N);

func = @(X) 2*X.*cos(X.^2).*exp(sin(X.^2)) + 14;

limit = func(X);

x = 4*rand(1,N);

y = 25*rand(1,N);

figure(1)

hold on

scatter(x,y,10,'markerfacecolor','b');

Lv = y < func(x); % Logical Vector Based On 'func' Value At Each 'x'

scatter(x(Lv),y(Lv),10,'MarkerFaceColor','r','Markeredgecolor','r')

plot(X,limit,'k-','linew',1.3)

.

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Haseeb Hashim 2022-4-11

Hi Great work. Can you please explain these lines expecially the first one

Lv = y < func(x);

scatter(x(Lv),y(Lv),10,'MarkerFaceColor','r','Markeredgecolor','r')

Star Strider 2022-4-11

Thank you!

Sure!

The ‘Lv’ variable is a logical vector that calculates the value of ‘func’ at each ‘x’ value and compares that result with the corresponding ‘y’ value. If that ‘y’ value is less than ‘func(x)’, that value of ‘Lv’ is set to true. (It definitely helps that ‘func’ is an anonymous function in your original code, making this straightforward.)

The scatter call just after that uses ‘Lv’ to refer to the individual ‘x’ and ‘y’ values, plotting only those that are true as defined by ‘Lv’.

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Answer 2

MJFcoNaN 2022-4-11

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1693650-i-want-to-change-the-color-of-the-markers-in-scatter-plot-which-are-below-the-function-line#answer_940040

在 MATLAB Online 中打开

You can try this:

clc

clear

close all

d = 4;

N = 1000;

X = linspace(0,d,N);

func = @(X) 2*X.*cos(X.^2).*exp(sin(X.^2)) + 14;

limit = func(X);

x = 4*rand(1,N);

y = 25*rand(1,N);

ind_r = y < limit;

c=zeros(N,3);

% red

c(ind_r, 1)=1;

% blue

c(~ind_r, 3)=1;

figure(1),hold on

h = scatter(x,y,10,c);

plot(X,limit,'k-','linew',1.3)

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Haseeb Hashim 2022-4-11

Now I get it we cant check the particular random against every number of function value because in this case the random numbers greater than the greatest number in function values will be turned blue otherwise they will be all read

MJFcoNaN 2022-4-11

Why do you make both x and y random?

If your task allows one random value, for example x=X, it may give out a more "reasonable" result, which achieves the same algorithm as the other answer.

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