How to fix "Index exceeds the number of array elements (1)"?

% degree of freedom
dof=6;

% Properties
a=1;
EI=1000;
EA=10^8;
L=[2*a 2*a a];
psi=[-90 0  90];

a1=[0 0 0 0 0 0;  0 0 0 0 0 0; 0 0 0 0 0 0; 1 0 0 0 0 0; 0 1 0 0 0  0; 0 0 1 0 0 0];
a2=[1 0 0 0 0 0;  0 1 0 0 0 0; 0 0 1 0 0 0; 0 0 0 1 0 0; 0 0 0 0 1 0; 0 0 0 0 0 1];
a3=[0 0 0 1 0 0;  0 0 0 0 1 0; 0 0 0 0 0 1; 0 0 0 0 0 0; 0 0 0 0 0 0; 0 0 0 0 0 0];
 
for i=1:length(L)
psi = psi(i);
L = L(i);

To=[cosd(psi) sind(psi) 0; -sind(psi) cosd(psi) 0; 0 0 1]; 
Tg=[To zeros(3); zeros(3) To];
       
k_bar=stiffness(dof, EI, EA, L);

k=Tg'*k_bar*Tg;
end

Function

function [k]= stiffness(dof, EI, EA, L)

my=EA/EI*L^2;

if dof == 6
    k=EI/L^3*[my 0 0 -my 0 0;...
            0 12 -6*L 0 -12 -6*L;...
            0 -6*L 4*L^2 0 6*L 2*L^2;...
            -my  0 0 my 0 0;...
            0 -12 6*L 0 12 6*L;...
            0 -6*L 2*L^2 0 6*L 4*L^2];
        
elseif dof == 4
    k=EI/L^3*[12 -6*L -12 -6*L;...
            -6*L 4*L^2 6*L 2*L^2;...
            -12 6*L 12 6*L;...
            -6*L 2*L^2 6*L 4*L^2];
        
elseif dof == 2
    k=EI/L^3*[1 -1;...
              -1 1];
end

Answer 1

[Stephane Dauvillier]

Hi,

In you code, first you define L as followed:

L=[2*a 2*a a];

Then, you redifine it to:

L = L(i); % where i is 1

After that L is a scalar and not a vector. SO Next time MATLAB reached the line

L = L(i); % this time i = 2

Since L isn't a vector of 3 number but just 2*a it doesn't works.

Don't overwrite L and it will be fine

Answer 2

[Torsten]

for i=1:length(L)
  psi0= psi(i);
  L0 = L(i);
  To=[cosd(psi0) sind(psi0) 0; -sind(psi0) cosd(psi0) 0; 0 0 1]; 
  Tg=[To zeros(3); zeros(3) To]; 
  k_bar=stiffness(dof, EI, EA, L0);
  k=Tg'*k_bar*Tg;
end