companion matrix
A=companion(p)
:p polynomial or vector of polynomials : :A square matrix :
Returns a matrix A with characteristic polynomial equal to p if p is monic. If p is not monic the characteristic polynomial of A is equal to p/c where c is the coefficient of largest degree in p.
If p is a vector of monic polynomials, A is block diagonal, and the characteristic polynomial of the ith block is p(i).
s=`poly`_(0,'s');
p=`poly`_([1,2,3,4,1],'s','c')
`det`_(s*`eye`_()-companion(p))
`roots`_(p)
`spec`_(companion(p))