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Converting A Set Of Roots To A Descending Polynomial
 Syntax `poly(z)` See Also zero2pol

Vector Argument
If z is a vector, `poly` returns a row vector `p` that corresponds to a descending polynomial `p[x]` which is zero at each of the elements of z where z is an integer real, double-precision, or complex column vector; that is ```      p[z ] = 0 for i = 1, . . . , n         i ```where `n` is the length of the vector z. The return has length `n+1` and the first element of the return value is 1. If the imaginary part of z is zero, the return value has type double-precision, otherwise the return value is complex.

Matrix Argument
If z is a square matrix , `poly` returns the polynomial that has zeros at the eigen values of z; i.e., ```      poly(eigen(z)) ```
Example
We can compute the product ```      x^2 - 1 = (x + 1) * (x - 1) ```which has the descending polynomial representation ```      [ 1 , 0 , -1 ] ```by ```      z = [-1, +1]      poly(z) ``` which returns ```      [ 1 , 0 , -1 ] ```