Excel Minverse function has truncation errors, and I would like to use
Gaussian Reduction to solve my eqn ( A.X = Y ) without using matrix
inversion.
I understand the theory and the maths - has anyone done this in MSExcel, or
has any ideas how I might do this?

[Basically, it involves Mmult with a triangular matrix to reduce terms below
the diagonal to zeros, until you then solve 'by inspection' from the bottom
up. Triangle matrix is similar to the identity matrix, but with one key
value replacing one of the zeros]