I have tried to solve a full linear system of approx 3 millions equation and 3 uknown.
If I try to solve the system (A\y) using mldivide i get:
Warning: Rank deficient, rank = 1, tol = 4.893629e+05.
And the results are completely wrong
However when forming the normal equation system (A'*A) x = A'*y the solver runs perfectly fine which is not surprising. (I know that in general is less numerically stable but in this case works fine)
From the documentation I read mldivide should use the QR solver on rectangular matrices. If i try to call QR on the A matrix I get:
Error using qr
Requested 3107227x3107227 (71934.3GB) array exceeds maximum array size preference.
My question are: what is mldivive trying to do? why it says that a rank deficecy is present?