Matrices with different numbers of equations

I'm supposed to construct a system of equations (Ax=b) matrix that will change depending on the number of equations given. For the forces on a bridge structure, I have equations for the first 4 and the last 4 rows of 'A'. I know how to make a matrix with these but depending on the number of nodes (N) in the structure, the number of equations will change. I'm told 'A' will be a 2N x 2N matrix and 'x' will be a 2N x 1 vector and 'b' is a 2N x 1 vector of constants. I know the equations that are dependent on the number of nodes have to utilize a loop. How would I initialize the 'A' and 'b' matrix with the zeros function manually?

Answer 1

[John D'Errico]

You know the size of the matrix. You already know you need to use zeros to initialize it.

A = zeros(2*N,2*N);
b = zeros(2*N,1);

You might want to read the help, especially when you already know what you want to do.