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

*To*: mathgroup at smc.vnet.net*Subject*: [mg55151] Re: How to use "Solve" to get only real number solutions?*From*: Peter Pein <petsie at arcor.de>*Date*: Mon, 14 Mar 2005 03:43:56 -0500 (EST)*References*: <d114lb$e18$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

PengYu.UT at gmail.com wrote: > 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[2])/(3*Pi)), x] > Hi Peng, you can either select the reals after computation of all solutions: Select[x /. Solve[intensity[x, 0, 200, 50] == 3/10*(1/4 + 32/(9*Pi^2) + (4*Sqrt[2])/(3*Pi)), x], Im[Chop[N[#]]] == 0 &] or use Reduce: Reduce[intensity[x, 0, 200, 50] == 3/10*(1/4 + 32/(9*Pi^2) + (4*Sqrt[2])/(3*Pi)), x, Reals] -- Peter Pein Berlin