compan

Companion matrix

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Syntax

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

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Open Script

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

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

A =

     0     7    -6
     1     0     0
     0     1     0

The eigenvalues of A are the polynomial roots.

eig(A)

ans =

   -3.0000
    2.0000
    1.0000

See Also

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Introduced before R2006a

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