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compan
Companion matrix
A=compan(u)
A = compan(u)
returns the corresponding companion matrix whose first row is -u(2:n)/u(1), where u is a vector of polynomial coefficients. The eigenvalues of compan(u) are the roots of the polynomial.
The polynomial 
has a companion matrix given by
u = [1 0 -7 6]
A = compan(u)
A =
0 7 -6
1 0 0
0 1 0
The eigenvalues are the polynomial roots:
eig(compan(u))
ans =
-3.0000
2.0000
1.0000
This is also roots(u).
eig Eigenvalues and eigenvectors
poly Polynomial with specified roots
polyval Polynomial evaluation
roots Polynomial roots