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    <div class="moz-cite-prefix">For the second point, specially since
      there are almost as many<br>
      constraints as variables, it may be worthwhile to take the Hessian<br>
      with respect to only the directions in the kernel of the
      constraints.<br>
      For example, if you are working in 20-dimensional Euclidean space,<br>
      with 18 constraints, that leaves an essentially 2-dimensional
      optimization<br>
      problem, and you only really need a 2x2 Hessian, not a 20x20
      Hessian.<br>
      You can choose two orthogonal directions in the kernel of the
      constraints,<br>
      and construct the 2x2 Hessian of Lagrangian wrt them, viewing this
      either<br>
      as directional derivatives or change of coordinates.<br>
      <br>
      I don't know what amount of SW changes this would need, but it<br>
      seems it would be generally useful.<br>
      <br>
      Cheers,<br>
      Norm<br>
      <br>
      <br>
      On 04/08/2013 06:38 AM, Ingrid Hallen wrote:<br>
    </div>
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      <div dir="ltr">Thanks for the suggestions!<br>
        <br>
        Regarding the first, I think it might not be so efficient for my
        problem, having<br>
        almost as many constraints as variables. But I might give it a
        try. Perhaps<br>
        one can modify the code for sparse_hess in some clever way ...<br>
        <br>
        Regarding the second I am unfortunately clueless as to how one
        could<br>
        exploit that fact.<br>
        <br>
        Kind regards,<br>
        <br>
        Ingrid<br>
        <br>
        <br>
        <div>
          <hr id="stopSpelling">Date: Sun, 7 Apr 2013 15:31:50 -0700<br>
          From: <a class="moz-txt-link-abbreviated" href="mailto:normvcr@telus.net">normvcr@telus.net</a><br>
          To: <a class="moz-txt-link-abbreviated" href="mailto:adol-c@list.coin-or.org">adol-c@list.coin-or.org</a><br>
          Subject: Re: [ADOL-C] Evaluating Hessian of Lagrangian<br>
          <br>
          <div class="ecxmoz-cite-prefix">Perhaps you can trace L as a
            function of both x and lambda.<br>
            Then when you need the hessian,<br>
            calculate the hessian only with respect to x.<br>
            Not sure if this is better/worse than what you suggested.<br>
            <br>
            When using the Hessian of the Lagrangian, you will
            eventually be restricting<br>
            attention to the kernel of your constraints.&nbsp; Do you know if
            this fact<br>
            would offer a simplification to how the hessian could be
            computed?<br>
            <br>
            Norm<br>
            <br>
            <br>
            On 04/05/2013 04:02 AM, Ingrid Hallen wrote:<br>
          </div>
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            <div dir="ltr">Hi,<br>
              <br>
              I'm doing non-linear optimization with IPOPT. For this,
              I'm using ADOL-C<br>
              to compute the Hessian of the Lagrangian<br>
              <br>
              L(x,lambda) = f(x) + sum_{i}lambda_{i}h_{i}(x),<br>
              <br>
              where x are the variables, lambda the Lagrange multipliers
              and <br>
              f(x) and h_{i}(x) objective and constraint functions.<br>
              <br>
              What I'm doing in my code is the following (omitting
              details):<br>
              <br>
              // **********************<br>
              <br>
              // Trace Lagrangian function<br>
              trace_on(tag);<br>
              <br>
              for(i=0;i&lt;n;i++) {<br>
              &nbsp;&nbsp;&nbsp; xad[i] &lt;&lt;= x[i];<br>
              }<br>
              <br>
              Lagrangian(xad, lambda);<br>
              <br>
              Lad &gt;&gt;=L;<br>
              <br>
              trace_off();<br>
              <br>
              // Evaluate Hessian of the Lagrangian<br>
              repeat = 0;<br>
sparse_hess(tag,n,repeat,x,&amp;nnz,&amp;rind,&amp;cind,&amp;values,&amp;options)<br>
              <br>
              // ***********************<br>
              <br>
              This works fine, but is not so efficient. One reason is
              that, since lambda changes, <br>
              the Lagrangian function has to be retaped every time the
              Hessian is needed and so it <br>
              appears that I cannot set repeat = 1 when calling
              sparse_hess.<br>
              <br>
              One way to circumvent this problem could perhaps be to
              trace the objective<br>
              and constraint functions individually and then construct
              the Hessian of<br>
              the Lagrangian using multiple calls to sparse_hess, but is
              there a<br>
              more convenient way to do it? <br>
              <br>
              Sincerely,<br>
              <br>
              Ingrid<br>
              <br>
            </div>
            <br>
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