Array indices must be positive integers or logical values.

code was working then it stopped, been at this for hours need some help

d = 0.1;
L = 2;
r = d/2;
ne = 8;
le = L/ne; % Assuming constant element length
A = pi*r^2;
p = 0.95;
E = 10^6;
nodes = linspace(0, L, ne+1);
elements = zeros(ne, 2);
for i = 1:ne
    elements(i, :) = [i, i+1];
end
properties = E*A/le*ones(ne, 3); % Properties matrix: [E, A, le]
K = zeros(ne+1);
for i = 1:ne
    k = properties(i, 1)*[1, -1; -1, 1]/properties(i, 3);
    K(elements(i, :), elements(i, :)) = K(elements(i, :), elements(i, :)) + k;
end

F = zeros(ne+1, 1);
F(end) = -1000;
K([1, end], :) = 0;
K(1, end) = 1;
K(1, end) = 1;

% part a
displacement = u(end);
reaction= -K(1,:)*u;

disp(displacement)
disp(reaction)

% % part b
% F = zeros(ne+1, 1);
% F(end)=F(end)-1000;
% K([1, end], :) = 0;
% K(1, 1) = 1;
% K(end, end) = 1;
% 
% displacements = u(end);
% reactions= -K(1,:)*u;
% 
% disp(displacements)
% disp(reactions)

Answer 1

[Voss]

The variable u is not defined in your code, but if it exists in your workspace and is empty, then the line

displacement = u(end);

would produce the error you reported.