How to create a matrix whose elements are a function of previous elements

I have an initial matrix of [1 2 4; 1 4 3] and am wanting to have this matrix gain additional rows by a certain amount given by the user wherein for each additional row, the values of the elements on that row are +2 from the values two rows before. So 2 additional rows from the initial matrix would provide [1 2 4; 1 4 3; 3 4 6; 3 6 5].

Answer 1

[Adam Danz]

This solution has two "inputs", initialMatrix and nRows and produces the output matrix out which has the same number of rows specified by nRows (unless nRows is less than the number of rows in the initial matrix).

% Inputs
initialMatrix = [1 2 4; 1 4 3]; % must have at least 2 rows
nRows = 7;  % number of desired rows in the output matrix

% compute additional rows
nRowsToAdd = nRows - height(initialMatrix); 
padlength = nRowsToAdd+mod(nRowsToAdd,2); % will be even 
delta = repelem((2:2:padlength)',2,1);
lastRows = repmat(initialMatrix(end-1:end,:), padlength/2, 1);
resultMatrix = lastRows + delta;

% Output
out = [initialMatrix; resultMatrix(1:nRowsToAdd,:)]

out = 7×3

1 2 4 1 4 3 3 4 6 3 6 5 5 6 8 5 8 7 7 8 10

[Lily Micallef]

Thank you very much!