Matrix define using for loop

How to define the following matrix (penta diagonal) using for loop?

[Walter Roberson]

Why use a for loop when Bruno already showed you a vectorized solution?

[mathru]

In this matrix, the diagonal value is -4. But for a generalized form of this matrix, I have to use an expression "1/(i*dr)" where dr is the increment along x direction. That's why I need to use for loop.

Answer 1

[KSSV]

Read about diag.

A = -4*ones(9,1) ; 
B = [1 1 0 1 1 0 1 1] ; 
C = ones(1,6) ; 

iwant = diag(C,-3)+ diag(B,-1) + diag(A) +diag(B,1) + diag(C,3)  

[mathru]

Hi KSSV, thanks for your code. Here is my generalized matrix. Can you please have a look?

[KSSV]

You can proceed like this:

% define the constants 
F0 = rand ; 
S = rand ; 
dr = 1 ; 
%
A = (2+4*F0)*ones(1,9) ; 
B = F0*ones(8,1) ; B(3:3:end) = 0 ; 
id = [2 2 2 3 3 3 ] ; 
C = -F0-S./(dr*id) ; 
id = [3 3 3 4 4 4 ] ; 
D = -F0+S./(dr*id) ;

iwant = diag(D,-3)+diag(B,-1)+diag(A)+diag(B,1)+diag(C,3) ;