# compan

Companion matrix

A = compan(u)

## Description

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.

## Examples

collapse all

Compute the companion matrix corresponding to the polynomial $\left(x-1\right)\left(x-2\right)\left(x+3\right)={x}^{3}-7x+6$.

u = [1 0 -7 6];
A = compan(u)
A = 3×3

0     7    -6
1     0     0
0     1     0

The eigenvalues of A are the polynomial roots.

eig(A)
ans = 3×1

-3.0000
2.0000
1.0000