<div dir="ltr"><div><div>Hi Run,<br><br></div>Try to set a bigger value of "nu_min," such as O(10^2) lower than your "tol" value.<br></div><div>I think default value for "nu_min" is 1e-10 or 1e-12 which I do not remember from top of my head.<br>
<br></div><div>Let me know if this helps.<br><br>Thanks.<br></div><div><div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Apr 5, 2013 at 9:00 AM, <span dir="ltr"><<a href="mailto:ipopt-request@list.coin-or.org" target="_blank">ipopt-request@list.coin-or.org</a>></span> wrote:<br>
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Today's Topics:<br>
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1. Question about the too many iteration in Ipopt (Run Zhu)<br>
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<br>
Message: 1<br>
Date: Thu, 4 Apr 2013 12:09:13 -0400<br>
From: Run Zhu <<a href="mailto:zhu.run@husky.neu.edu">zhu.run@husky.neu.edu</a>><br>
To: <a href="mailto:ipopt@list.coin-or.org">ipopt@list.coin-or.org</a><br>
Subject: [Ipopt] Question about the too many iteration in Ipopt<br>
Message-ID:<br>
<CABvdRVzPrFswmtA3WqH2pX5hu8whJsZStPmW01RWcsiP=<a href="mailto:MtE_Q@mail.gmail.com">MtE_Q@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="iso-8859-1"<br>
<br>
Dear All,<br>
<br>
I am PhD student of Northeastern University, specializing in computational<br>
material science. My current work is to determine the equilibrium position<br>
of dislocation in the metal bar under tensile load. This is achieved by<br>
minimizing interaction energy of dislocation. The optimization model, for a<br>
single degree of freedom, is<br>
<br>
find: x<br>
min: W = - ln ( x^2 + a^2) - b*x<br>
st: lb < x < ub<br>
<br>
where optimization variable, x, is the position of dislocation; objective<br>
function, W, is the interaction energy; a and b are constant, and lb and ub<br>
are the upper and lower bound. The attached figure shows the x versus W.<br>
The boundary is also considered.<br>
<br>
The initial value x0 is the equilibrium position in last loading step,<br>
which is pretty close to the optimal x*<br>
<br>
The ipopt works perfectly well when the number of degree of freedom is low,<br>
like 50. However, when the no. of optimization variable, x, is greater than<br>
100, ipopt takes many search around x*, up to 500 times. The gradient is<br>
analytically available for this problem and the minimum is always there.<br>
But I cannot figure out how this happens.<br>
<br>
If you have any idea to this situation. Please feel free to contact me so<br>
that I can provide more details.<br>
<br>
Thanks<br>
<br>
Cheers<br>
<br>
Run Zhu<br>
<br>
<br>
--<br>
Run Zhu, PhD student<br>
Department of Mechanical and Industrial Engineering<br>
Northeastern University<br>
Boston, MA 02115<br>
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End of Ipopt Digest, Vol 100, Issue 4<br>
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</blockquote></div><br><br clear="all"><br>-- <br>Jesus Loves you,<br>Young (Youngsoo).
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