MATLAB Function Reference 
Form least squares augmented system
Syntax
Description
S = spaugment(A,c)
creates the sparse, square, symmetric indefinite matrix S = [c*I A; A' 0]
. The matrix S
is related to the least squares problem
The optimum value of the residual scaling factor c
, involves min(
svd
(A))
and norm
(r)
, which are usually too expensive to compute.
S = spaugment(A)
without a specified value of c
, uses max
(max(
abs
(A)))/1000
.
Note
In previous versions of MATLAB, the augmented matrix was used by sparse linear equation solvers, \ and /, for nonsquare problems. Now, MATLAB performs a least squares solve using the qr factorization of A instead.

See Also
sparse  spconvert 