keep getting an error message

i keep getting an error mesage when im trying to write a script for school. Error message reads "Index in position 1 exceeds array bounds. Index must not exceed 2.Error in gp (line 29)

dx = x(node2, 1) - x(node1, 1);" how can i fix this problem.

% Define the truss geometry
L = 0.3; % Length of horizontal and vertical members (m)
Lsqrt2 = sqrt(2) * L; % Length of inclined members (m)
E = 100e9; % Young's modulus (N/m²)
A = 1e-4; % Cross-sectional area (m²)
% Define the node coordinates
x = [0, 0.3, 0.3, 0; 0, 0, 0.3, 0.3,];
% Define the connectivity matrix
connectivity = [1, 2, 3, 1; 1, 4, 3, 2; 2, 4, 1, 3];
% Define the external loads
Fx13 = [10000; 0; 0; 0];
Fx14 = [-10000; 0; 0; 0];
Fy13 = [0; 10000; 0; 0];
Fy14 = [0; -10000; 0; 0];
% Initialize the element stiffness matrix
k = zeros(4, 4);
% Loop over the elements
for i = 1:size(connectivity, 1)
    % Extract the node numbers for the current element
    node1 = connectivity(i, 1);
    node2 = connectivity(i, 2);
    % Calculate the cosine and sine of the element angle
    dx = x(node2, 1) - x(node1, 1);
    dy = x(node2, 2) - x(node1, 2);
    cos_theta = dx / sqrt(dx^2 + dy^2);
    sin_theta = dy / sqrt(dx^2 + dy^2);
    % Calculate the element stiffness matrix
    k(1, 1) = (E * A * cos_theta ^ 2) / L;
    k(2, 2) = (E * A * sin_theta ^ 2) / L;
    k(1, 2) = (E * A * cos_theta * sin_theta) / L;
    k(2, 1) = k(1, 2);
    % Assemble the global stiffness matrix
    global_stiffness_matrix = zeros(size(x, 1) * 2);
    global_stiffness_matrix(2 * node1 - 1, 2 * node1 - 1) = global_stiffness_matrix(2 * node1 - 1, 2 * node1 - 1) + k(1, 1);
    global_stiffness_matrix(2 * node1 - 1, 2 * node1) = global_stiffness_matrix(2 * node1 - 1, 2 * node1) + k(1, 2);
    global_stiffness_matrix(2 * node1, 2 * node1 - 1) = global_stiffness_matrix(2 * node1, 2 * node1 - 1) + k(2, 1);
    global_stiffness_matrix(2 * node1, 2 * node1) = global_stiffness_matrix(2 * node1, 2 * node1) + k(2, 2);
    global_stiffness_matrix(2 * node2 - 1, 2 * node2 - 1) = global_stiffness_matrix(2 * node2 - 1, 2 * node2 - 1) + k(1, 1);
    global_stiffness_matrix(2 * node2 - 1, 2 * node2) = global_stiffness_matrix(2 * node2 - 1, 2 * node2) + k(1, 2);
    global_stiffness_matrix(2 * node2, 2 * node2 - 1) = global_stiffness_matrix(2 * node2, 2 * node2 - 1) + k(2, 1);
end

Index in position 1 exceeds array bounds. Index must not exceed 2.

Answer 1

[Torsten]

x is a 2x4 matrix.

So as soon as node1 or node2 in the lines

% Calculate the cosine and sine of the element angle
dx = x(node2, 1) - x(node1, 1);
dy = x(node2, 2) - x(node1, 2);

are greater than 2, MATLAB will error.

Maybe you mean

% Calculate the cosine and sine of the element angle
dx = x(1, node2) - x(1, node1);
dy = x(2, node2) - x(2, node1);

?

[Hector Meza]

but now im getting this error

Index in position 1 exceeds array bounds. Index must not exceed 4.

Error in gp (line 47)

global_stiffness_matrix(2 * node2 - 1, 2 * node2 - 1) =

global_stiffness_matrix(2 * node2 - 1, 2 * node2 - 1) + k(1, 1);

[Torsten]

Initialize

global_stiffness_matrix = zeros(size(x, 2) * 2);

outside the for-loop.