# compan

## Purpose

Companion matrix.

## Synopsis

    A = compan(p)

## Description

`A = compan(p)` where `p` is a vector of polynomial coefficients, returns the corresponding companion matrix whose first row is `-p(2:n)/p(1)`.

The eigenvalues of `compan(p)` are the roots of the polynomial.

## Examples

The polynomial

has a companion matrix given by

    p = [1  0  -7  6]
    A = compan(p)

    A =
        0    7   -6
        1    0    0
        0    1    0

The eigenvalues are the polynomial roots:

    eig(compan(p)) =

        -3.0000
         2.0000
         1.0000

This is also `roots(p)`.

## See Also

    eig, poly, polyval, roots

(c) Copyright 1994 by The MathWorks, Inc.