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

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

[Walter Roberson]

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]

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

Answer 1

[Star Strider]

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)

.

[Haseeb Hashim]

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]

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’.

Answer 2

[MJFcoNaN]

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)

[Haseeb Hashim]

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]

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.