[Ipopt] irregular iteration counts of small scale problem

[dongming jin]

dear all:
I'm solving a nonlinear problem which has 3 constraints and 12 variables with ipopt. But the iteration count  gets larger than 1000 and ipopt can't find an optimal solution. Can anyone help me out?


the problem is showed below:
objective function:
pow(10, 6)*(x[6] + x[7] + x[8] + x[9] + x[10] + x[11])
constraints:
 (-x[2] * cos(x[0])) / (0.075556*x[4]) + pow(x[2], 2) / 0.075556 + x[6] - x[7]=0
 (-x[3] * cos(x[1])) / (0.075556*x[5]) + pow(x[3], 2) / 0.075556 + x[8] - x[9]=0
 0.1<-x[2] * cos(x[0]) / (0.075556*x[4]) - x[3] * cos(x[1]) / (0.075556*x[5]) + 1 / 0.075556*(1 / pow(x[4], 2) + 1 / pow(x[5], 2)) + x[10] - x[11]<0.3099
variables:
-pi/2<x[0],x[1]<pi/2;  0.95<x[2],x[3]<1.05;  0.9<x[4],x[5]<1.1;  0<x[6]~x[11]<10^7


I guess it has something to do with the symmetrical constraints. When i set the lower bound of the third constraints to zero, ipopt found the optimal solution in the 15th iteration.and I  paste the main program in the appendix for reference. 
I would appreciate it if anyone can give me some advice.


dongming jin


 
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