# Finding gcd of polynomials with extra parameter in Maple

My problem is that I have two functions in two variables, say $x$ and $y$. The functions are both polynomials in $x$, but sometimes $y$ appears in an exponent. What I want to do is find the gcd of these functions as if they are viewed as polynomials in $x$. However, when I use the gcd command it says it can not do it because the arguments must be polynomials. I have tried redefining the functions as just functions in $x$ (i.e. $h(x)$ $= f(x,y))$, but it still does not work. So is there anyway for me to get Maple to look at these functions as polynomials in $x$ and thus find the gcd? Or is there some other way I could do this?

Edit:

The polynomials I am working with a little complicated but here they are in general:

First, we define:

$$a(i,x,y) = (-1)^i(\binom{2y-1}{i-1}x^y+ \binom{2y-1}{i})$$

Now, our set of polynomials are:

$$f(i,x,y) = \binom{2y}{i-1} + \sum_{j=1}^{y}\binom{2y-j}{i-1}a(j,x,y) + \sum_{j=1}^{y-1}\binom{y-j}{i-1}a(y-j,x,y)x^j+\binom{0}{i-1}x^y$$

Where we use the convention $\binom{n}{k} =0$ if $k > n$.

What I am interested in determining is the gcd of $f(1,x,y)$ and $f(2,x,y)$. But Maple does not view them as polynomials as $y$ appears in the exponent, as stated above.

• Have you tried putting in some specific values for $y$ to see how the gcd changes? – abiessu Jul 23 '13 at 15:51
• I have tried all integer values of y up to 500 and I always get the same gcd, which is what I expected. I just want to now show that that is the case all the time. – user85140 Jul 23 '13 at 16:09

How are you passing the info?

From the help:

gcd(a, b, 'cofa', 'cofb')

The optional third argument cofa is assigned the cofactor a/gcd(a, b).

The optional fourth argument cofb is assigned the cofactor b/gcd(a, b).

Examples:

gcd(x^2-y^2,x^3-y^3,c,d);
-y+x
c;
x + y
d;
2          2
x  + x y + y

• The problem is that Maple isn't recognizing the function as polynomial since it has y in the exponent. However it is a polynomial in x, so I want to try and just find the gcd as a polynomial in x. – user85140 Jul 23 '13 at 16:12
• Please, post here your pols. – Sigur Jul 23 '13 at 16:14