Extract upper triangle of matrix (using vector different from diagonal)

Hello, I am trying to extract some data from a matrixt, wherein the upper "triangle" contains the signal I am interested in. I can extract a big chunk of ut using triu(), the issue is the lower bound is not a diagonal, but steeper than the diagnonal (for every row there is about 1.5 columns if that makes sense), causing the upper section to be cut using triu(). Is there a way of doing it with a nested for loop or the like? I am banging my head against a wall here. See pictures for reference.

Answer 1

[Cameron]

If you have the data in a form of X and Y data points, you can do something like this

x = randi([220,800],100,1); %100 random x data points between 220 and 800 
y = randi([200,600],100,1); %100 random y data points betwen 200 and 600
myindx = y - 0.5*x >= 0; %index which is above a line from x1 = 400, y1 = 200,
%x2 = 800, y2 = 400. This gives a slope of 0.5 and y intercept of 0.
NewX = x(myindx); %x values only above your myindx line
NewY = y(myindx); %y values only above your myindx line
plot(x,y,'o',... 
    NewX,NewY,'o',...
    [400,800],[200,400],'-k')

[Philipp Brunnbauer]

this is great, will try it! Thanks Cameron

[Philipp Brunnbauer]

Hey Cameron, I had to modify the script a bit and now have a working version of it - thanks a lot!