unable to rotate the plot

% Rotate the axes
theta = 3*pi/4; % Set theta.
fprintf('Rotate the axes...\n');
[x_mat_rotated, y_mat_rotated] = rotation(x_mat, y_mat, theta);
plot_function(x_mat_rotated, y_mat_rotated);
fprintf('Finished.');

The above is from my hw mfile, which i should add extra code in another mfile to run it,

% Write the code here
% Hint: you can use matrix product to solve the new coordinate for every
% point.
R = [cos(theta), sin(theta); -sin(theta), cos(theta)];
B = [x_mat ; y_mat]
A = R*B
x_mat_new = A(1,:)
y_mat_new = A(2,:)
end
%-------------------------------------------------------

I write the above code, and it results in a wrong graph, how can i fix it? The figure should be a rotated parabolathe wrong figure that i generate

[DGM]

It's hard to troubleshoot code that's not there, but this much works.

% some fake data
x_mat = linspace(-2,2,100);
y_mat = x_mat.^2;

% transform the data
theta = pi/4; % Set theta.
[x_mat_rotated, y_mat_rotated] = rotation(x_mat, y_mat, theta);

% plot both
plot(x_mat,y_mat,':'); hold on; grid on
plot(x_mat_rotated, y_mat_rotated);
axis equal

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function [x_mat_new, y_mat_new] = rotation(x_mat,y_mat,theta)
R = [cos(theta), sin(theta); -sin(theta), cos(theta)];
B = [x_mat; y_mat];
A = R*B;
x_mat_new = A(1,:);
y_mat_new = A(2,:);
end

Depending on your frame of reference, you can swap the signs on the sin() terms to change the rotation direction.

Answer 1

[Diego Caro]

Are you sure you're plotting the right thing? Look at this other example using your code.

y = 0:0.1:10;
x = y;

theta = pi/2; % Changed theta to visualize better rotation
R = [cos(theta), sin(theta); -sin(theta), cos(theta)];
B = [x; y];
A = R*B;

figure
hold on
plot(x,y)
plot(A(1,:),A(2,:))
legend('Original line','Rotated line')

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