The Interior Point Nonlinear Programming Solver -- Experimental

Example 7.2: Solving Unconstrained Optimization Problems

Although the IPNLP solver is suited for solving constrained NLP problems, it can solve efficiently unconstrained problems too. We demonstrate its ability by considering the following relatively large unconstrained NLP problem:

\displaystyle\mathop{\rm minimize}f(x) = \sum_{i=1}^{n-1} ( - 4 x_{i} + 3.0) + \sum_{i=1}^{n-1} (x_{i}^2 + x_{n}^2)^2

where n=5000. To solve this problem, you can write the following SAS code:

    proc optmodel;
       number N=5000;
       var x{1..N} init 1.0;
       
       minimize obj = sum {i in 1..N - 1} ( - 4 * x[i] + 3.0)  + 
                    sum {i in 1..N - 1} (x[i]^2 + x[N]^2)^2;
 
       solve with ipnlp;
    quit;
 

The problem and solution summaries are shown in Output 7.2.1.

Output 7.2.1: Problem Summary and Solution Summary
The OPTMODEL Procedure

Problem Summary
Objective Sense Minimization
Objective Function obj
Objective Type Nonlinear
   
Number of Variables 5000
Bounded Above 0
Bounded Below 0
Bounded Below and Above 0
Free 5000
Fixed 0
   
Number of Constraints 0



The OPTMODEL Procedure

Solution Summary
Solver IPNLP
Objective Function obj
Solution Status Optimal
Objective Value 0
Iterations 12
   
Infeasibility 0
Optimality Error 5.3537499E-8




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