### 2.24.20 Coefficients of a polynomial defined by its roots : `pcoeff pcoef`

`pcoeff` (or `pcoef`) takes as argument a list of
the roots of a polynomial *P*.

`pcoeff` (or `pcoef`) returns a univariate polynomial having
these roots,
represented as the list of it’s coefficients by decreasing order.

Input :

`pcoef([1,2,0,0,3])`

Output :

`[1,-6,11,-6,0,0]`

i.e. (*x*−1)(*x*−2)(*x*2)(*x*−3)=*x*5−6*x*4+11*x*3−6*x*2.