Error code: "Index in position 2 exceeds array bounds (must not exceed 1)." when running code for two-element spring system

I am using Matlab to code a two-element spring in FEA, based on Peter I. Kattan book's : MATLAB Guide to Finite Elements: An Interactive Approach. In it, there is an example numbered as Example 2.1, which includes codes as follows

Here is the example question:

And here is the stiffness matrix calculations:

Here is global stiffness matrix calculation

However, when I run K=SpringAssemble(K,k1,1,2), I get this error message

Can anyone help me out on this one? Thank you.

[VBBV]

For the last function you also need to pass y as the input value

function y = SpringElementForces(y,u)
%u.
y = y*u;
end

Answer 1

[VBBV]

K(i,i) = K(i,i) + y(1,1);
K(i,j) = K(i,j) + y(1,2);

[VBBV]

k is scalar assigned to variable y defined inn the function

function y = SpringElementStiffness(k)
 y = [k -k;-k k]
end

but you are trying to access the nonexistent elements by using

k(1,2)

You need to use y in place of k

[VBBV]

Also pass the matrix y as input to the function

function y = SpringAssemble(K,y,i,j)