#### 6.56 arguments of a function, op function (19.9.00)

I wanted to know if there is a function that will return the argument to a RootOf function.
Like an inverse RootOf function.

Example:

G := Q=RootOf(_Z^2+4*_Z+5);
G := Q=RootOf(_Z^2+4*_Z+5)
rhs(G);
RootOf(_Z^2+4*_Z+5)

now, I’d like to get at the quantity `_Z^2+4*_Z+5`

so I could pass it to a discrim
function.

Try

op(1,RootOf(_Z^2+4*_Z+5));

You could try the op function, to break down the root of function. The op function breaks
down larger complex expressions into components, so used in this case, it would look
something like this:

G := Q=RootOf(_Z^2+4*_Z+5);
2
G := Q = RootOf(_Z + 4 _Z + 5)
op(rhs(G));
2
_Z + 4 _Z + 5

You can assign that last result to a variable and pass it to the discrim function, or to any
other function that you want.

`op(%);`

or, for other forms of RootOf,

`op(1,%);`

In this case, `op( * )`

will work, but if something has multiple arguments, you can use
`op( N, * )`

to select the Nth operand:

> op( f( a, b, c ) );
a, b, c
> op( 1, f( a, b, c ) );
a
> op( 2, f( a, b, c ) );
b
> A := RootOf( _Z^2+4*_Z+5 ):
> op( 1, A );
2
_Z + 4 _Z + 5

although it is probably a good idea to change the `_Z`

to some other variable as `_Z`

is
recognized as being special in a number of cases in Maple:

> eval( op( 1, A ), _Z = x );
2
x + 4 x + 5

You could always just enter the routine:

> ExtractRootOf := proc(A::specfunc(anything,RootOf), y::algebraic)
eval( op( 1, A ), _Z = y );
end:
> ExtractRootOf( RootOf( _Z^2+4*_Z+5 ), x );
2
x + 4 x + 5
> ExtractRootOf( RootOf( _Z^2+4*_Z+5 ), x^2 );
4 2
x + 4 x + 5

to do this for you automatically.