[Ipopt] Problem has too few degrees of freedom

[Stefan Vigerske]

Hi,

the message tells you that your system has more constraints than 
variables. That is, if you increase your N_s too much, you will have 
more equations than what could be satisfied with your number of 
variables. This somehow assumes that your equations are not redundant, 
which would be bad in general anyway.

Best is if you reformulate your problem, i.e., remove redundant 
equations. If none of them is redundant, then your problem is obviously 
infeasible.

Stefan

On 09/30/2013 08:11 AM, Novalio Daratha wrote:
> Hi guys,
>
> I am trying to solve a NLP problem.
>
> min f(x)
> s.t.
>
> g(x,p_i)=0  \forall i=1...N_s
> h(x)>=0
>
> where x represents control variables and p_i represents the i-th set of
> parameters.
> for N_s<=4, Ipopt can solve the problem. Otherwise, IPOPT gave the
> following message:
>
>
> ******************************************************************************
> This program contains Ipopt, a library for large-scale nonlinear
> optimization.
>   Ipopt is released as open source code under the Common Public License
> (CPL).
>           For more information visit http://projects.coin-or.org/Ipopt
> ******************************************************************************
>
> NOTE: You are using Ipopt by default with the MUMPS linear solver.
>        Other linear solvers might be more efficient (see Ipopt
> documentation).
>
>
> This is Ipopt version 3.8.0, running with linear solver mumps.
>
> Number of nonzeros in equality constraint Jacobian...:  1743324
> Number of nonzeros in inequality constraint Jacobian.:   225000
> Number of nonzeros in Lagrangian Hessian.............:   540888
>
> Exception of type: TOO_FEW_DOF in file
> "f:\stefan\nbBuildDir\Ipopt\releases-3.8.0\Ipopt\src\Interfaces\IpIpoptApplication.cpp"
> at line 788:
>   Exception message: status != TOO_FEW_DEGREES_OF_FREEDOM evaluated false:
> Too few degrees of freedom (rethrown)!
>
> EXIT: Problem has too few degrees of freedom.
>
>
> Is there anyway to avoid this problem?
>
> Thank you very much for your kind attention.
>
> I look forward for your favorable reply.
>
>
> SIncerely Yours,
>
> Novalio Daratha
>
>
>
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