How can change transparency and thickness of a line in Matlab

I have written the code in Matlab by using scatter. However, I cannot change alpha value or opacity, or transparency of the line. Can anyone guide how can I do it just by using scatter plot?

x=[1:140];
sz=1;
H=scatter(x(1),y(1),sz)
set(H,'MarkerFaceColor','blue');
set(H,'MarkerEdgeColor','blue');

hold on
for i=2:140
    sz=sz+1;
   H=scatter(x(i),x(i),sz) 
   set(H,'MarkerFaceColor','blue');
   set(H,'MarkerEdgeColor','blue');
end

I have already tried the following code but it gave me error

set(H,'MarkerFaceAlpha',.2);
set(H,'MarkerEdgeAlpha',.2);

[Rik]

Can you show the entire error message? Because I just tried it in R2017a and I didn't get an error.

Answer 1

[José-Luis]

Provided you have a reasonably recent version of Matlab:

 p1 = plot(rand(10,1),'r-','LineWidth',5); hold on
 p2 = plot(rand(10,1),'r-','LineWidth',2);
 p1.Color(4) = 0.25;
 p2.Color(4) = 0.75;

[Maximiliano Rivera]

Why this work? If a run p1.Color it gave me a 1x3 vector, there's not a 4th component.

[Chad Greene]

I second Maximiliano's question: Why exactly does this work? And is there a way to query the alpha value after it is set?

It's interesting that I can set

p1.Color(4) = 0.25; 

and it sets the alpha value perfectly without complaint. But now when I try to query the alpha value by typing simply

p1.Color(4) 

I get this error message:

Index exceeds the number of array elements (3). 

Where exactly is the alpha information stored?

[Tarek Saati]

thnks man, saved the day... didn't get on my mind before

[Egor Ananyev]

The plot.Color(4) solution seems to be posted everywhere, but does not seem to work on more recent version of Matlab (R2021a here).

I tried the following two ways, and neither worked:

plt1.Color(4) = 0.1;  % does not work in R2021a
plt1.Color = [plt1.Color 0.1];  % does not work in R2021a

[Jiri Hrdlicka]

Same here, the undocumented 4-element color spec does not seem to work, anymore (R2021a).

[rui sun]

The color editing still works for me on 2021a.

data = randn(100,2);
hline = plot(data);
for i=1:length(hline)
    hline(i).Color = [hline(i).Color 0.1];  % alpha=0.1
end