[Ipopt] IPOPT takes very long before the first iteration

Uwe Nowak uwe.nowak at itwm.fhg.de
Mon Sep 28 07:51:40 EDT 2009

```Hello!

I am using IPOPT and really like the solver. But with larger problem
instances the solver takes very long time before the first iteration.

Below there is the output. After the first line ("This is IPOPT...") the
solver takes (estimated) 350 CPU seconds.

What does IPOPT do there? Is there a way to speed this part of IPOPT up?
The Iterations itself are fast enough.

I am using IPOPT to successively solve nonlinear problems that have similar,
but not equal structure. So I usually expect only few iterations to be
necessary.

Thank you,
Uwe Nowak

------------------------- OUTPUT ------------------------------

This is Ipopt version 3.7.0, running with linear solver ma27.

Number of nonzeros in equality constraint Jacobian...: 196
Number of nonzeros in inequality constraint Jacobian.: 13624
Number of nonzeros in Lagrangian Hessian.............: 0

Total number of variables............................: 180
variables with only lower bounds: 0
variables with lower and upper bounds: 0
variables with only upper bounds: 0
Total number of equality constraints.................: 49
Total number of inequality constraints...............: 1703
inequality constraints with only lower bounds: 1703
inequality constraints with lower and upper bounds: 0
inequality constraints with only upper bounds: 0

[...]

Number of Iterations....: 15

[...]

Number of objective function evaluations = 18
Number of objective gradient evaluations = 16
Number of equality constraint evaluations = 18
Number of inequality constraint evaluations = 18
Number of equality constraint Jacobian evaluations = 16
Number of inequality constraint Jacobian evaluations = 16
Number of Lagrangian Hessian evaluations = 0
Total CPU secs in IPOPT (w/o function evaluations) = 392.561
Total CPU secs in NLP function evaluations = 8.939

EXIT: Optimal Solution Found.

```

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