How can i change the 1st row 1st column and last row last column values in a tridiagonal matrix

 n=5;
A=zeros(n,n);
for i=1:n
    if (i>1) 
        A(i-1,i)=-100;
    end
    A(i,i)=300;
    if (i<n)
        A(i+1,i)=-100;
    end

end

I wrote the code above to create a tridiagonal matrix. I need to separate the 1st row 1st column variable and the last row last column variable, so that i can assign a different value for these two variable's but im not sure how to write a statement to do this task.

Answer 1

[Are Mjaavatten]

A(1,1) = 17;A(end,end) = 23;

You can create your original matrix without using a loop:

n = 5;
A = diag(ones(1,n))*300-diag(ones(1,n-1)*100,-1)-diag(ones(1,n-1)*100,1);