subroutine to solve linear algebraic equations - fewer unknowns than equations

[Bsbosa.com]

Hi I am looking for subroutines to solve linear algebraic equations - fewer unknowns than equations. This subroutine should find the mean of each unknowns and standard deviations. This means that there will be as many as the number of sets of simultaneous equations from N to form M simultaneous equations (permutation). M- number of unknowns, N is the number of equations. N>M.

Thanks