inv_coeff - build a polynomial matrix from its coefficients
P=inv_coeff(Mp,k), when k is compatible with Mp size, returns a polynomial matrix of degree k. C=[C0,C1,...,Ck] and P= C0 + C1*x +... +Ck*x^k.
A=int(10*rand(2,6)) // Building a degree 1 polynomial matrix P=inv_coeff(A,1) norm(coeff(P)-A) // Using default value for degree P1=inv_coeff(A) norm(coeff(P1)-A)