       Re: How to use "Solve" to get only real number solutions?

• To: mathgroup at smc.vnet.net
• Subject: [mg55135] Re: [mg55132] How to use "Solve" to get only real number solutions?
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Mon, 14 Mar 2005 03:43:35 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```intensity[x_] := 1/4+(2*Cos[(Pi*x)/100])/Pi+
(4*Cos[(Pi*x)/100]^2)/Pi^2-
(2*Cos[(3*Pi*x)/100])/(3*Pi)-
(8*Cos[(Pi*x)/100]*Cos[(3*Pi*x)/100])/(3*Pi^2)+
(4*Cos[(3*Pi*x)/100]^2)/(9*Pi^2);

Off[Solve::ifun];

Select[Chop[Solve[
intensity[x] == 0.3*(1/4+32/(9*Pi^2)+
(4*Sqrt)/(3*Pi)),x]],
FreeQ[x/.#,Complex]&]

{{x -> -47.4207},{x -> 47.4207}}

Bob Hanlon

>
> From: "PengYu.UT at gmail.com" <PengYu.UT at gmail.com>
To: mathgroup at smc.vnet.net
> Date: 2005/03/13 Sun AM 04:57:54 EST
> To: mathgroup at smc.vnet.net
> Subject: [mg55135] [mg55132] How to use "Solve" to get only real number solutions?
>
> Hi All
>
> For example I have the following function and I want to find the
> solution of the quation shown below. But Mathematica showns not only
> real number solutions. Do you know how to restrict the solutions to
> only real numbers. Thanks!
>
> Best wishes,
> Peng
>
> intensity[x_, Î´_, p_, Î»_] := 1/4 + (2*Cos[(Pi*x)/100])/Pi +
> (4*Cos[(Pi*x)/100]^2)/Pi^2 - (2*Cos[(3*Pi*x)/100])/(3*Pi) -
>  (8*Cos[(Pi*x)/100]*Cos[(3*Pi*x)/100])/(3*Pi^2) +
> (4*Cos[(3*Pi*x)/100]^2)/(9*Pi^2)
>
> Solve[intensity[x, 0, 200, 50] == 0.3*(1/4 + 32/(9*Pi^2) +
> (4*Sqrt)/(3*Pi)), x]
>
>

```

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