Convert from a symbolic polynomial : e2r symb2poly

### 2.24.2 Convert from a symbolic polynomial : `e2r symb2poly`

`e2r` or `symb2poly` takes as argument a symbolic polynomial and either a symbolic variable name (by default `x`) or a list of symbolic variable names.
`e2r` or `symb2poly` transforms the polynomial into a list (dense representation of the univariate polynomial, coefficients written by decreasing order) or into a sum of monomials (sparse representation of multivariate polynomials).
Input :

`e2r(x```^```2-1)`

or :

`symb2poly(x```^```2-1)`

or :

`symb2poly(y```^```2-1,y)`

or :

`e2r(y```^```2-1,y)`

Output :

`1,0,-1`

Input :

`e2r(x```^```2-x*y+y, [x,y])`

or :

`symb2poly(x```^```2-x*y+2*y, [x,y])`

Output :

`%%%{1,[2,0]%%%}+%%%{-1,[1,1]%%%}+%%%{2,[0,1]%%%}`