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<div class="moz-cite-prefix">Thanks,<br>
<br>
looks like my best option is to reformulate, as most likely I'm
introducing redundant equations. I'm curious about the
"dependency_detector" options, as I don't see them on the options
list
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<a href="http://www.coin-or.org/Ipopt/documentation/node59.html">http://www.coin-or.org/Ipopt/documentation/node59.html</a>
is there a particular reference page in the manual or are these
options undocumented. My guess is that the dependency checker is
associated with the particular linear solver used ?<br>
<br>
Ian.<br>
<br>
<br>
<br>
On 03/05/2013 08:22 AM, Stefan Vigerske wrote:<br>
</div>
<blockquote cite="mid:5135F181.8030802@math.hu-berlin.de"
type="cite">Hi,
<br>
<br>
the fixed_variable_treatment only decides how to treat variables
that are fixed via its bounds. If you have equations that fix
variables, it would be better if you could reformulate them as
fixing of variables.
<br>
<br>
As far as I know, there is no well tested algorithm in Ipopt to
deal with overdetermined systems of equations. You could try the
dependency_detector options. They try to detect a set of equations
that are dependent and remove them from the problem before passing
it to Ipopt. Maybe you are lucky and it works for you.
<br>
<br>
I cannot comment on the Matlab interface.
<br>
<br>
Stefan
<br>
<br>
On 03/01/2013 09:45 PM, Ian Washington wrote:
<br>
<blockquote type="cite">Hello IPOPT community,
<br>
<br>
I am trying to pose an NLP where the number of equality
constraints is
<br>
greater than the number of decision variables (i.e., an
over-determined
<br>
system) and the solver immediately exits with a
<br>
Not_Enough_degrees_Of_Freedom error. Basically there are some
equality
<br>
constraints that fix some of the variables.
<br>
<br>
Clearly my problem is formulation related and I could
reformulate the
<br>
equality constraints to two inequality constraints using a small
<br>
tolerance, but I rather not if possible.
<br>
<br>
Note, I'm using the matlab interface to ipopt and directly
specifying
<br>
all constraints/sparsity pattern, but I'm using the
limited-memory
<br>
Hessian approximation.
<br>
<br>
My first question: does the matlab interface expose all possible
ipopt
<br>
solver options to the user ? (I assume so, since I didn't
receive any
<br>
errors)
<br>
<br>
Second, I tried to change the fixed_variable_treatment to
relax_bounds
<br>
but it didn't seem to help. I thought this would at least
prevent the
<br>
Not_Enough_degrees_Of_Freedom error flag from occurring.
<br>
<br>
Note, I've tried this problematic formulation using knitro and
the
<br>
solver proceeds with only a warning stating that there are more
equality
<br>
constraints than variables. Also, snopt handles the problem with
no issues.
<br>
<br>
Does anyone have any ideas to get around this problem.
<br>
<br>
Thanks,
<br>
Ian.
<br>
<br>
<br>
<br>
<br>
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</blockquote>
<br>
</blockquote>
<br>
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