Row equivalence 31/03
Summary
Let M, M0 be two matrices.
We say that M is row equivalent to M0 if M, M0 have the same size and M0 can be obtained from M by one or more ERO’s.
We indicate this by writing M ∼ M0.
It is obvious that, for any matrices M, M0, M00, we have
• M ∼ M,
• M ∼ M0, M0 ∼ M00 ⇒ M ∼ M00.
But because each type of ERO can be reversed, we also have
• M ∼ M0 ⇒ M0 ∼ M.
These three properties mean that ∼ is an equivalence relation.
Now suppose that M = ( A | B) and M0 = ( A0|B0) represent linear systems with B, B0 column vectors.
Theorem. M ∼ M0 iff the two systems AX = B and A0X = B0 have the same solutions.
If M ∼ M0 then r (M) = r (M0) and r (A) = r (A0) because row reduction preserves the rank of matrices. By (RC1), solutions only exist if all these ranks are all equal.