[Ipopt] Question about the too many iteration in Ipopt (Run Zhu)

[Youngsoo Choi]

Hi Run,

Try to set a bigger value of "nu_min," such as O(10^2) lower than your
"tol" value.
I think default value for "nu_min" is 1e-10 or 1e-12 which I do not
remember from top of my head.

Let me know if this helps.

Thanks.


On Fri, Apr 5, 2013 at 9:00 AM, <ipopt-request at list.coin-or.org> wrote:

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> ----------------------------------------------------------------------
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> Message: 1
> Date: Thu, 4 Apr 2013 12:09:13 -0400
> From: Run Zhu <zhu.run at husky.neu.edu>
> To: ipopt at list.coin-or.org
> Subject: [Ipopt] Question about the too many iteration in Ipopt
> Message-ID:
>         <CABvdRVzPrFswmtA3WqH2pX5hu8whJsZStPmW01RWcsiP=
> MtE_Q at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Dear All,
>
> I am PhD student of Northeastern University, specializing in computational
> material science. My current work is to determine the equilibrium position
> of dislocation in the metal bar under tensile load. This is achieved by
> minimizing interaction energy of dislocation. The optimization model, for a
> single degree of freedom, is
>
> find: x
> min: W = - ln ( x^2 + a^2) - b*x
> st: lb < x < ub
>
> where optimization variable, x, is the position of dislocation; objective
> function, W, is the interaction energy; a and b are constant, and lb and ub
> are the upper and lower bound. The attached figure shows the x versus W.
> The boundary is also considered.
>
> The initial value x0 is the equilibrium position in last loading step,
> which is pretty close to the optimal x*
>
> The ipopt works perfectly well when the number of degree of freedom is low,
> like 50. However, when the no. of optimization variable, x, is greater than
> 100, ipopt takes many search around x*, up to 500 times. The gradient is
> analytically available for this problem and the minimum is always there.
> But I cannot figure out how this happens.
>
> If you have any idea to this situation. Please feel free to contact me so
> that I can provide more details.
>
> Thanks
>
> Cheers
>
> Run Zhu
>
>
> --
> Run Zhu, PhD student
> Department of Mechanical and Industrial Engineering
> Northeastern University
> Boston, MA 02115
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-- 
Jesus Loves you,
Young (Youngsoo).
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