# Why are certain matrices referred to as n x n?

Nusc
Why are certain matrices referred to as n x n?

I rarely see anything refer to an m x m matrix, on what circumstance do we see this? Or why isn't this used for anything?

Homework Helper
Yes, "rectangular" matrices represent linear transformations from Rm to Rn. The problem is that linear transformations from spaces of different dimensions can't be 1 to 1 or onto- that is, they don't have inverses. It is basically the same problem as solving m equations in n unknowns. If m< n, there are not enough equations and many different solutions. If n< m, there are too many equations- in general there is no solution. It is only n equations in n unknowns that have solutions.

neurocomp2003
in math n is usually the first symbol used to define the mth term... thus u see M_nxn rather than M_mxm. Its like
[] "i" is usually the first counter followed by j,k,l
[] "a" is coefficient followed by b,c,d
[] "x" for spatial quantities.
[] F for functions G,H
[] theta for angles
etc. who designed them i don't know but its the way you usually learn.