Selects diagonals of a matrix.
diags([1,2,3;4,5,6;7,8,9], [2,-1])
| mtx | The matrix, the diagonals of which are to be selected |
| offset | The indices of the diagonals to be selected (optional). Negative (resp. positive) indices denote subdiagonals (resp. superdiagnoals). |
| return value | The matrix with the diagonals in its rows. |
Returns a matrix, the rows of which are the diagonals indexed by offset. The diagonals of different lengths are padded with zeros to form a matrix in a way that, except for this padding, the function acts as an inverse for the function diag, i.e. superdiagonals at the tail, and subdiagonals at the front: diags(diag(D,d),d) ~ D, and for a diagonal square matrix M: diag(diags(M,d),d) = M hold.
The second argument is optional. The lack of it is equivalent to offset = [0].