How to divide a plot into different regions

I have a random set of points which I intend to plot in different colours depending on their region. I am struggling on what function/equation i would need to create the lines/regions. An example of the regions i have plotted below. I would be looking to plot different colours in the 4 different regions i have quickly shown in the image below.

Answer 1

[Image Analyst]

Get the y values for each line for the x value of your point that you want to plot. So your point's y value will either be less than or greater than the y value of the line. For each line you will know if it's above or below, so just assign the color of the plot based on that.

if y < yBlackLine && y < yRedLine % y is the y of the point.
  % Region 1.  Plot point as red.
  plot(x, y, 'ro');
elseif y < yBlackLine && y > yRedLine
  % Region 2  Plot point as green.
  plot(x, y, 'go');
elseif y > yBlackLine && y < yRedLine
  % Region 3  Plot point as blue.
  plot(x, y, 'bo');
elseif y > yBlackLine && y > yRedLine
  % Region 4  Plot point as black
  plot(x, y, 'ko');
end

[Andy]

Thank you, i don't think i made it too clear in my first post. The main problem i had was to plot the lines. For the image above i just used plot and specified the x and y values. That is not going to allow me to get all x and y values along that line, i would need some equation to create my line?

[Image Analyst]

First, get the endpoints of the lines. Then plot them with line():

line([x1, x2], [y1, y2], 'Color', 'r');

Once you have that, you can calculate the slope

slope = (y2-y1) / (x2-x1);

Then the y value for any x value is

y = slope * (x-x1) + y1

Do that for both lines. Plug in the x value for the point you want to plot to find the y value for each line. Then determine if it's above or below the y value of the point you want to plot, like I showed.