Using external functions through ASL in pyomo, solving with ipopt

[Viacol0916]

Hi, I'm planning to write a corresponding ASL structural adapter function for a C++ function I've written as an external function. Then I compile it into a .dll file, call it via ExternalFunction in Pyomo and solve it with IPOPT.

I'm now experiencing the following error message from IPOPT.It may seem a bit confusing.

ERROR: Solver (ipopt) returned non-zero return code (3221226505)
ERROR: See the solver log above for diagnostic information.
Error during solving: Solver (ipopt) did not exit normally

Here is the C++ function.

double Srk::CalcMassEntropyLiquidMixture(
        std::vector<double> &molefraction,
        double &temperature,
    	double &pressure)

Here's the adapter function I write that corresponds to the ASL structure.

real calc_mass_entropy_liquid_mixture(arglist *al) {
    int n = al->n;
    std::vector<double> molefraction = {al->ra, al->ra + n - 3};
    double temperature = al->ra[n-2];
    double pressure = al->ra[n-1];

    real entropy;
    entropy = Srk::CalcMassEntropyLiquidMixture(molefraction, temperature, pressure);
    return entropy;  // return answer
}


void funcadd(AmplExports *ae){
    int t = FUNCADD_REAL_VALUED;
    addfunc("calc_mass_entropy_liquid_mixture", (rfunc)calc_mass_entropy_liquid_mixture, t, -1, NULL);
}

Here's the pyomo part.

def create_model():
    m = pyo.ConcreteModel()
    m.name = 'Example 1: Eason'
    m.z = pyo.Var(range(3), domain=pyo.Reals, initialize=2.)
    m.x = pyo.Var(range(3), initialize={0: 0.3, 1: 0.3, 2: 0.4})
    m.temperature = pyo.Var(initialize=260.0)
    m.pressure = pyo.Var(initialize=1823850)
    m.ext_fcn = pyo.ExternalFunction(library='myfunctions.dll', function='calc_mass_entropy_liquid_mixture')	#Here calls the imported function
    m.obj = pyo.Objective(expr=(m.z[0]-1.0)**2 + (m.z[0]-m.z[1])**2 + (m.z[2]-1.0)**2 + (m.x[0]-1.0)**4 + (m.x[1]-1.0)**6)
    m.c1 = pyo.Constraint(expr=100 + m.ext_fcn(m.x[0], m.x[1], m.x[2], m.temperature, m.pressure) == 66)	#it becomes a part of the constraints here
    m.c2 = pyo.Constraint(expr=m.z[2]**4 * m.z[1]**2 + m.z[1] == 8+pyo.sqrt(2.0))
    return m
model = create_model()
solver = pyo.SolverFactory('ipopt')

try:
    result = solver.solve(model, tee=True)
    print("Solver status:", result.solver.status)
    print("Solver termination condition:", result.solver.termination_condition)
except Exception as e:
    print("Error during solving:", e)

Interestingly, when I replace

m.c1 = pyo.Constraint(expr=100 + m.ext_fcn(m.x[0], m.x[1], m.x[2], m.temperature, m.pressure) == 66)

with

m.c1 = pyo.Constraint(expr=100 + m.ext_fcn(m.x, m.temperature, m.pressure) == 66)

in pyomo, the error is

Error during solving: Cannot emit InvalidNumber(<pyomo.core.expr.numvalue.NonNumericValue object at 0x0000018BA49F0430>) in compiled representation
The InvalidNumber was generated by:
	<pyomo.core.expr.numvalue.NonNumericValue object at 0x0000018BA49F0430> (<class 'pyomo.core.expr.numvalue.NonNumericValue'>) is not a valid numeric type

I have no idea how to fix it, so I ask for help here.

[svigerske]

There is a good advise already:

ERROR: See the solver log above for diagnostic information.

So what does the Ipopt log say?

[Viacol0916]

thanks for your reply, I think this is what ipopt is reporting as an error:

ERROR: Solver (ipopt) returned non-zero return code (3221226505)

I tried printing the log file but IPOPT fails before generating any output, resulting in not outputting the log file.

solver.options['print_level'] = 6
solver.options['output_file'] = 'ipopt.out'

[svigerske]

I have no clue. Maybe capture the .nl file that Pyomo generates, and run this with the Ipopt executable. If there is still no reasonable log, then do some debugging. Probably the library with the external function isn't found by ASL in Ipopt.

[Viacol0916]

Sorry for the late reply, thank you very much for your answer, I will try it as you suggested.

[Viacol0916]

I've solved the problem. Compiling the .dll library with gcc did the trick! I used to compile it with Developer Command Prompt for VS, but it failed.