Section: Optimization and Curve Fitting
    p = poly(r)
when r is a vector, is a vector whose elements are the coefficients 
of the polynomial whose roots are the elements of r.  Alternately,
you can provide a matrix
    p = poly(A)
when A is an N x N square matrix, is a row vector with 
N+1 elements which are the coefficients of the
characteristic polynomial, det(lambda*eye(size(A))-A).
Contributed by Paulo Xavier Candeias under GPL.
poly
--> A = [1,2,3;4,5,6;7,8,0]
A = 
 1 2 3 
 4 5 6 
 7 8 0 
--> p = poly(A)
p = 
    1.0000   -6.0000  -72.0000  -27.0000 
--> r = roots(p)
r = 
   12.1229 
   -5.7345 
   -0.3884