Hey,
Check this:
% Constants
sigma_0 = 2;
theta_deg = [0, 90, 180, 270]; % Degrees
theta_rad = deg2rad(theta_deg); % Convert degrees to radians
% Variable
r = 1:0.1:2;
% Pre-allocate sigma_r for efficiency
sigma_r = zeros(length(r), length(theta_rad));
% Calculate sigma_r for each theta
for i = 1:length(theta_rad)
theta = theta_rad(i);
ksi = 1./r;
sigma_r(:, i) = (1/2.*sigma_0.*(1-(ksi.^2))) - (1/2.*sigma_0.*(1+(3.*(ksi.^4))-(4.*(ksi.^2))).*cos(2.*theta));
end
% Plotting
figure; % Create a new figure
hold on; % Hold on to plot multiple lines
colors = ['r', 'g', 'b', 'k']; % Colors for each theta
for i = 1:length(theta_rad)
plot(r, sigma_r(:, i), 'Color', colors(i), 'DisplayName', sprintf('\\theta = %d°', theta_deg(i)));
end
hold off;
xlabel('r');
ylabel('\sigma_r');
title('\sigma_r vs. r for \theta = 0, 90, 180, and 270 degrees');
legend('show');
grid on;
