Description: 
The function GaussJordan(A,b) allows to solve simultaneoulsy different linear systems with the same coefficient matrix A using the GaussJordan algorithm.
The output of GaussJordan(A,b) is either a vector x if b is a vector, or a matrix nbyp of of x's the different solutions vectors of the equations
Ax1 = b1, Ax2 = b2, ..., Axp = bp
