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MathGroup Archive 2003

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RE: Re: Help to solve numerical equation

  • To: mathgroup at
  • Subject: [mg43786] RE: [mg43753] Re: Help to solve numerical equation
  • From: "David Park" <djmp at>
  • Date: Sat, 4 Oct 2003 02:05:05 -0400 (EDT)
  • Sender: owner-wri-mathgroup at


If you can narrow down the domain to a reasonable value then Ted Ersek's
RootSearch package from MathSource will get both roots.


RootSearch[lhs==rhs,{x,xmin,xmax}] tries to find all numerical solutions to
the equation (lhs==rhs) with values of x between xmin and xmax.

eq = 0.5*Exp[x*200] + 0.21*Exp[x*500] +
       0.1*Exp[x*110] + 0.07*Exp[x*(15)] +
       0.018*Exp[x*(-16)] + 0.002*Exp[x*(-263)] - 1;

RootSearch[eq == 0, {x, -1, 1}]
{{x -> -0.0232796}, {x -> 0.00042907}}

Plot[eq, {x, -0.03, 0.004}]

David Park
djmp at

From: Jean-Claude Poujade [mailto:poujadej at]
To: mathgroup at

bobhanlon at (Bob Hanlon) wrote in message
news:<blgiif$feh$1 at>...
> NSolve is used primarily with polynomial equations.  Use FindRoot.
> eq=0.5*Exp[x*200]+0.21*Exp[x*500]+
>       0.1*Exp[x*110]+0.07*Exp[x*(15)]+
>       0.018*Exp[x*(-16)]+0.002*Exp[x*(-263)]-1;
> FindRoot[eq==0,{x,.0004}]
> {x -> 0.00042907}
> Bob Hanlon

Right! But FindRoot doesn't "see" there's another root...


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