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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. :-)
Doc missing
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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. :-)
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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) => [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....
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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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