Re: Using FindRoot in complex funtion

*To*: mathgroup at smc.vnet.net*Subject*: [mg71924] Re: Using FindRoot in complex funtion*From*: "tatsec" <markelbbs at tom.com>*Date*: Mon, 4 Dec 2006 06:38:51 -0500 (EST)*References*: <ekucvg$830$1@smc.vnet.net>

Sorry,the program have format's error,the correct program is below,but it can't solve the problem; I used FindRoot,the Prgram is f[x_] := With[{sigma = Sqrt[2], L = 30}, Integrate[(2^(1/2 - L/2)*sigma^(-1 - L)*Abs[t]^((-1 + L)/2)*BesselK[(1 - L)/2, Abs[t]/(sigma^2)])/(Sqrt[Pi]*Gamma[L/2]), {t, 0, x}]]; With[{Pf = 0.000001}, eta = FindRoot[f[x] == (1/2 - Pf), {x, 50}]]; But it can't find the true root; So I used the function of RootSearch,the program is Needs["Ersek`RootSearch`"]; f[x_] := With[{sigma = Sqrt[2], L = 30}, Integrate[(2^(1/2 - L/2)*sigma^(-1 - L)*Abs[t]^((-1 + L)/2)*BesselK[(1 - L)/2, Abs[t]/(sigma^2)])/(Sqrt[Pi]*Gamma[L/2]), {t, 0, x}]]; With[{Pf=0.000001},eta = RootSearch[f[x] == (1/2 - Pf), {x, 50, 100}])]; The error Information is "RootSearch::vars: RootSearch was given an an equation with variables (t, x) when it expected to solve an equation where the only variable is x.",So anybody can solve this problem; But N[With[{sigma = Sqrt[2], L = 30, x = 55}, f[x]], 30] the result is 0.499996468582504966302482543641 I just used this software,anybody can help me? Thanks