Create a 2d coordinate system with areas separated by color

I want to categorize all the points in the range x=[0,1], y=[0,1], to two groups, and display these groups as painted areas in a 2d "graph".

I cannot express those groups as a function, they will be some binary relation and its complementary relation over the range.

General structure/pseudo code:

x = linspace(0,1,1000);
y = linspace(0,1,1000);

group1 = [];
group2 = [];

for i=1:1:length(x)
    for j=1:1:length(y)
        % check if (x,y) belongs to group1
        if belongs_to_group1(x(i),y(j))
            group1 = vertcat(group1, [x(i),y(j)]);
        else
            group2 = vertcat(group2, [x(i),y(j)]);
        end
    end
end

% plot colored categorization
plot(group1, 'red', group2, 'blue')
xlabel('x')
ylabel('y')
title('Red is group1, blue is group2')

Answer 1

[Divyam]

Hi @Tomer Tuchner,

After you determine the binary function to categorize the points, use the "filled" parameter of the "scatter" plot function to display these categorized group of points as painted areas.

% Define the grid of points
x = linspace(0, 1, 100);
y = linspace(0, 1, 100);

% Initialize groups
group1 = [];
group2 = [];

% Define the binary relation function
belongs_to_group1 = @(x, y) (x.^2 + (2*y).^2 < 0.2); 

% Categorize points
for i = 1:length(x)
    for j = 1:length(y)
        if belongs_to_group1(x(i), y(j))
            group1 = [group1; x(i), y(j)];
        else
            group2 = [group2; x(i), y(j)];
        end
    end
end

% Plot the categorized points
figure;
hold on;

% Plot group1 as red area
if ~isempty(group1)
    scatter(group1(:,1), group1(:,2), 5, 'r', 'filled', 'DisplayName','Group1');
end

% Plot group2 as blue area
if ~isempty(group2)
    scatter(group2(:,1), group2(:,2), 5, 'b', 'filled', 'DisplayName','Group2');
end

xlabel('x');
ylabel('y');
legend
hold off;

You can alternatively use the "fill" function for filling out the areas based on the binary function.

For more information regarding the "scatter" and "fill" functions, refer to the following documentation links:

• https://www.mathworks.com/help/matlab/ref/scatter.html?s_tid=doc_ta#btrj9jn-1-filled:~:text=%22filled%22%20%E2%80%94%20Option%20to%20fill%20interior%20of%20markers
• https://www.mathworks.com/help/matlab/ref/fill.html