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Re: Generated parameters

  • To: mathgroup at smc.vnet.net
  • Subject: [mg116275] Re: Generated parameters
  • From: Simon <simonjtyler at gmail.com>
  • Date: Wed, 9 Feb 2011 02:11:21 -0500 (EST)
  • References: <iir4g5$6ir$1@smc.vnet.net>

I think that what you want is only true if d>0.
Otherwise you have to worry about possible branch cuts.
These are explicitly given in the Mathematica because you asked
for dom=Reals.
Note that even though they follow from complex analysis, all solutions
provided are explicitly real.
Note that if you use dom=Complexes, then the result looks much
simpler, but is not guaranteed to be real.

On Feb 8, 9:04 pm, olfa <olfa.mra... at yahoo.fr> wrote:
> Hi Mathematica community,
> For this system:
> Reduce[v/d^(i/-2) == vP/d^(iP/-2) &&
>   (iP == -1 || iP == 0), {iP, vP}, Reals, Backsubstitution -> T=
rue]
>
> the output is:
> (iP == 0 && C[1] \[Element] Integers && d < 0 && i == -2 C[1] &&
>    vP == (-d)^-C[1] v)
> ||
>  (iP == 0 && C[1] \[Element] Integers &&
>    C[1] <= -1 && d < 0 && i == -2 C[1] &&
>    vP == (-d)^-C[1] v)
> ||
> (iP == 0 && C[1] \[Element] Integers &&
>    d < 0 && i == -2 C[1] && vP == -(-d)^-C[1] v)
>  ||
>  (iP == 0 &&
>    C[1] \[Element] Integers && C[1] <= -1 && d < 0 && i == -2 C=
[1] &&
>    vP == -(-d)^-C[1] v)
> ||
>  (d > 0 && iP == 0 &&
>    vP == d^(i/2) v)
>  ||
>  (d > 0 && iP == -1 && vP == d^(1/2 + i/2) v)
>
> 1)Why Reduce generates parameters for this example?
> 2) and how to avoid them knowing that for this system the solution
> that I hope to get is
>  ( iP == 0 && vP == d^(i/2) v)
> ||
>  ( iP == -1 && vP == d^(1/2 + i/2) v)
>
> Thank you.



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