#109 No describe(polydecomp)

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

Doc missing

Discussion

  • Raymond Toy

    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

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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....

     
  • Robert Dodier

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

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

    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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