Re: Creation and evaluation of polynomials

• To: mathgroup at smc.vnet.net
• Subject: [mg89450] Re: Creation and evaluation of polynomials
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Tue, 10 Jun 2008 03:38:26 -0400 (EDT)
• Organization: Uni Leipzig
• References: <g2j05j\$510\$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de

```Hi,

imaging that *we* have no function that is able to create
the polynomial p^5 + 3p^2 from the invalid Mathematica
input.

All your ToString[]/ ToExpression[] is complete nonsense.

But imaging that

polynomial[lst_, var_: x] := Plus @@ MapIndexed[#1*var^(#2[[1]]-1) &, lst]

create a polynomial, than

D[polynomial[{1, 0, 0, 0, 1, 0, 1}], x]

compute the derivative

and

NSolve[polynomial[{0, 2, 1}] == x, x]

will find the numerical roots.

Regards
Jens

jmgomezgoo at gmail.com wrote:
> Hi!
>
> Image we have a function that create a Polynomial:
>
> polynomial[{1,0,0,0,1,0,1,}] -> p^5 + 3p^2
>
> And we want to calulate roots and the derivate of this polynomial.
>
> I try with ToString[polynomial[{1,0,0,0,1,0,1}]] in order to use
> convert the polynomial expression to string first and later use
>
> ToExpression[]
>
> and calculate roots
>
> D[ToExpression[ToString[polynomial[{1,0,0,0,1,0,1}]], x]
>
> like the next examples:
>
> D[ToExpression["x^2+2x"], x]
>
> or
>
> NSolve[ToExpression["x^2+2x==x"], x]
>
>
> But ToString erase ^ symbol.
>
> Somebody knows how to solve it?
>
>
> Warm regards
> -jm
>
>
>

```

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