How to combine two matrices

Hello,

I want matrix d to go into matrix A.

Thanks in advance

n=4
A = 4*diag(ones(n^2,1)) - diag(ones(n^2-1,1),-1) - diag(ones(n^2-1,1),1)

d1=diag(-1*ones(n^2,1),-3);
d2=diag(-1*ones(n^2,1),3);

d=d1+d2

Answer 1

[Walter Roberson]

Where in A should d go?

Note that A is going to be an n^2 by n^2 array as you put something of length n^2 along the main diagonal, and the other two diagonals have had their length adjusted properly to be consistent.

Note that d is going to be an (n^2+3) by (n^2+3) array, as the length of the third diagonal is n^2, so the length of the second diagonal would be n^2 + 1 so the length of the first diagonal would be n^2 + 2 so the length of the main diagonal would be n^2 + 3.

So you cannot put d within A. You could put A within d.

What I suspect you want is to fix your sizes for d1 and d2, and then use

A = A + d

[Emilia]

I want the matrix to look like this.

[Walter Roberson]

You just have to correct the lengths for d1 and d2, and

A = A + d