# gfroots

Find roots of polynomial over prime Galois field

## Syntax

`rt = gfroots(f,m,p)`

rt = gfroots(f,prim_poly,p)

[rt,rt_tuple] = gfroots(...)

[rt,rt_tuple,field] = gfroots(...)

## Description

**Note**

This function performs computations in GF(p^{m}),
where p is prime. To work in GF(2^{m}), use
the `roots`

function with Galois arrays. For details,
see Roots of Polynomials.

For all syntaxes, `f`

is a polynomial
character vector or a row vector that gives the coefficients,
in order of ascending powers, of a degree-d polynomial.

`rt = gfroots(f,m,p)`

finds
roots in GF(`p^m`

) of the polynomial that `f`

represents. `rt`

is
a column vector each of whose entries is the exponential format of
a root. The exponential format is relative to a root of the default
primitive polynomial for GF(`p^m`

).

`rt = gfroots(f,prim_poly,p)`

finds
roots in GF(`p`

^{m}) of the
polynomial that `f`

represents. `rt`

is
a column vector each of whose entries is the exponential format of
a root. The exponential format is relative to a root of the degree-m
primitive polynomial for GF(`p`

^{m})
that `prim_poly`

represents.

`[rt,rt_tuple] = gfroots(...)`

returns
an additional matrix `rt_tuple`

, whose kth row is
the polynomial format of the root `rt(k)`

. The polynomial
and exponential formats are both relative to the same primitive element.

`[rt,rt_tuple,field] = gfroots(...)`

returns
additional matrices `rt_tuple`

and `field`

. `rt_tuple`

is
described in the preceding paragraph. `field`

gives
the list of elements of the extension field. The list of elements,
the polynomial format, and the exponential format are all relative
to the same primitive element.

**Note**

For a description of the various formats that `gfroots`

uses,
see Representing Elements of Galois Fields.

## Examples

Roots of Polynomials contains
a description and example of the use of `gfroots`

.

The code below finds the polynomial format of the roots of the
primitive polynomial 2 + x^{3} + x^{4} for GF(81).
It then displays the roots in traditional form as polynomials in `alph`

.
(The output is omitted here.) Because `prim_poly`

is
both the primitive polynomial and the polynomial whose roots are sought, `alph`

itself
is a root.

p = 3; m = 4; prim_poly = [2 0 0 1 1]; % A primitive polynomial for GF(81) f = prim_poly; % Find roots of the primitive polynomial. [rt,rt_tuple] = gfroots(f,prim_poly,p); % Display roots as polynomials in alpha. for ii = 1:length(rt_tuple) gfpretty(rt_tuple(ii,:),'alpha') end

## Version History

**Introduced before R2006a**