
Calling Sequence


compoly(r)
compoly(r, x)
compoly(r, {x, ... })


Parameters


r



polynomial

x



variable on which the composition will be made





Description


•

The function compoly returns a pair $p\left(x\right)$, $x=q\left(x\right)$ such that subs(x=q(x), p(x)) is equal to r, the input polynomial. If such a pair cannot be found, it returns FAIL. $p\left(x\right)$ and $q\left(x\right)$ are nonlinear polynomials and $q\left(x\right)$ has a lowdegree in x greater or equal to 1.

•

When compoly is called without additional arguments, it is equivalent to being called with a second argument which is indets(r). When the second argument is a set with more than one variable, then a multivariate composition is attempted. In this case, the result has the same form, but the second polynomial is multivariate, that is, $p\left(x\right)$, $x=q\left(x,...\right)$. For the multivariate case, the second polynomial, $q\left(x\right)$, may be of degree 1.

•

Note that the composition may not be unique. In particular, if $p\left(x\right)$, $x=q\left(x,...\right)$ is a composition, then we can find another $p\left(x\right)$ such that replacing $q\left(x,...\right)$ by $cq\left(x,\dots \right)+b$ will also result in a valid composition. This nondeterminacy is eliminated by selecting c and b such that the q polynomial has integer content 1 and its independent term is 0.



Examples


>

$\mathrm{compoly}\left({x}^{6}9{x}^{5}\+27{x}^{4}27{x}^{3}2{x}^{2}y\+6xy\+1\,x\right)$

${{x}}^{{3}}{}{2}{}{x}{}{y}{+}{1}{,}{x}{=}{{x}}^{{2}}{}{3}{}{x}$
 (1) 
>

$\mathrm{compoly}\left({x}^{4}3{x}^{3}x\+5\,x\right)$

>

$\mathrm{compoly}\left({x}^{2}\+2xy7x\+{y}^{2}7y\+16\right)$

${{x}}^{{2}}{}{7}{}{x}{+}{16}{,}{x}{=}{x}{+}{y}$
 (3) 
>

$\mathrm{compoly}\left({x}^{4}\+4{x}^{3}{y}^{3}\+6{x}^{2}{y}^{6}\+4x{y}^{9}\+{y}^{12}\+x\+{y}^{3}1\,\left\{x\,y\right\}\right)$

${{x}}^{{4}}{+}{x}{}{1}{,}{x}{=}{{y}}^{{3}}{+}{x}$
 (4) 


