closed
nobody
5
2005-11-16
2002-08-10
No

Doc missing

## Discussion

• Raymond Toy - 2002-08-18

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What does polydecomp do? What do you expect it to do.

Hard to give documentation for describe if I don't know what
it does. :-)

• Stavros Macrakis - 2002-08-19

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Polydecomp(Expr,Variable)

Consider Expr as a polynomial in Variable. Polydecomp
expresses Expr as the functional composition of one or more
polynomials.

For example, consider

p: expand(subst(x^3-x-1,x,x^2-a))

polydecomp(p,x) returns

[ x^2-a, x^3-x-1]

that is,

lambda([x],x^2-a)(x^3-x-1)

More trivially, polydecomp(x^6,x) =&gt; [x^3,x^2]

Decompositions like this are not unique. For example,
[x^2+2,x^2+1] (polydecomp's answer) is equivalent to
[x^2+2*x+3,x^2]. I am not sure how polydecomp chooses its
decompositions. I believe that only the last polynomial is
ever linear, but other than that....

• Robert Dodier - 2005-04-09
• labels: --> Documentation

• Robert Dodier - 2005-11-16
• status: open --> closed

• Robert Dodier - 2005-11-16

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Description given by Stavros as a comment on bug report
1340694 adapted into r1.18 of doc/info/Polynomials.texi.

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