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MathGroup Archive 2001

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RE: Simple Eval Question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31953] RE: [mg31883] Simple Eval Question
  • From: "Higinio Ramos" <higra at usal.es>
  • Date: Fri, 14 Dec 2001 04:21:15 -0500 (EST)
  • References: <200112091107.GAA18114@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

----- Original Message -----
From: ivo welch <ivo.welch at anderson.ucla.edu>
To: mathgroup at smc.vnet.net
Subject: [mg31953] [mg31883] Simple Eval Question


> I have a simple problem.  I want to numerically solve
>
>    Solve[  Integrate[ f[x,p]*g[x], {x,0,Infinity}] == V , p ]
>
> where f[] and g[] are defined functions, but the naive solution fails.
>
> W=1; g=0.5; q=0.1; V=2;
> fd[x_]:= PDF[ LogNormalDistribution[0,1],x ] ;
> Solve[ Integrate[ ((W +(x-p)*q)^g)/g * fd[x], { x, 0, Infinity } ]== V,
p ]
>
> Solve::"tdep": "The equations appear to involve the variables to be solved
\
> for in an essentially non-algebraic way."
>
> The correct answer seems to be 1.5652 .  How do I ask Mathematica to tell
me
> this number?
>
> (My ultimate goal is to plot the solved p as a function of q.)
>
> /iaw
>

W = 1; g = 0.5; q = 0.1; V = 2;
fd[x_] := PDF[ LogNormalDistribution[0, 1], x ] ;
In[13]:=
SetPrecision[

dRoot[ 
    Integrate[ ((W + (x - p)*q)^g)/g * fd[x], { x, 0, Infinity } ] == V, {p, 
      1.5} ], 20]


Out[13]=
{p -> 1.5652055223965051223}

H. Ramos




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