create a system matrix that had a "finite element" structure/property in matlab

To create a system matrix with a finite element structure in MATLAB, you typically follow these steps:

  1. Define the problem domain: Determine the geometry and boundaries of your system. Divide the domain into finite elements such as triangles or quadrilaterals.

  2. Assign element properties: Define material properties and other relevant properties for each element, such as conductivity or elasticity.

  3. Assemble the stiffness matrix: For each element, calculate the element stiffness matrix using the element properties and the shape functions. Then, assemble the element stiffness matrices to form the global stiffness matrix.

Here's an example code snippet to illustrate the process:

main.m
% Define the problem domain
x = [0 1 0 1];  % x-coordinates of the nodes
y = [0 0 1 1];  % y-coordinates of the nodes
elements = [1 2 3; 2 3 4];  % element connectivity

% Assign element properties
E = 1;  % Young's modulus
A = 1;  % cross-sectional area

% Assemble the stiffness matrix
numNodes = size(x, 2);
numElements = size(elements, 1);
numDOFs = numNodes * 2;  % number of degrees of freedom

K = zeros(numDOFs);  % initialize the system matrix

for elem = 1:numElements
    % Get the element connectivity
    nodes = elements(elem, :);
    x_elem = x(nodes);
    y_elem = y(nodes);
    
    % Calculate the element stiffness matrix
    [Ke] = calculateElementStiffness(x_elem, y_elem, E, A);
    
    % Assemble the element stiffness matrix into the global stiffness matrix
    for i = 1:3
        for j = 1:3
            K(2*nodes(i)-1, 2*nodes(j)-1) = K(2*nodes(i)-1, 2*nodes(j)-1) + Ke(2*i-1, 2*j-1);
            K(2*nodes(i), 2*nodes(j)) = K(2*nodes(i), 2*nodes(j)) + Ke(2*i, 2*j);
        end
    end
end

% Display the system matrix
disp(K);
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