Hi!, I don't know where to find it, but if you waant to work with Linear 
Algebra object, here at te University of Buenos Aires we did many things 
about it the hierarchy is something like this:

Tuple
Matrix
MatrixReducer
  GaussReducer
  EuclideanReducer
LinearBasis
LinearSubspace
LinearEquation
LinearSystem
LinearSystemSolver
LinearFOrm
LinearTransformation
....

Because the Linear Algebra works over  any field  we have:
ScalarsAmbient

We also have the ambients where the Linear Algebra objects live:
TupleAmbient
MatrixAmbient
PolynomialAmbient ..etc.

If you want something or everything of this stuff, please let me know an 
i'll send it to you (gzipped), as a change set.

PS.: The matrix protocol has #leftInverse message (if the matrix is 
invertible the LeftInverse is the inverse)


Regards.

 -- 
Eric Maximiliano Rodriguez Guevara
eguevara at dc.uba.ar