Advanced

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Custom Operations

Conditional Compilation

You can use Python's if, elif, and else to perform conditional compilation.

Let's say you have a model of a wing in steady state flow, and different models for the aerodynamics below and above a Reynolds number of 1,000,000. Depending on what condition you want to simulate, you could make the decision at compile time as to which submodel to add to your model:

if Re < 1000000:    self.add(SlowModel())else:    self.add(FastModel())

Only one model results in code generation because the condition is evaluated at compile time.

note

CSDL does not offer a way of performing conditional execution at run time.

Using Loops to Add Several Models

A model specification can be constructed programmatically at compile time, based on compile time constants (parameters).

class Example(Model):    def initialize(self):        self.parameters.declare('num_engines', default=2, types=int)        self.parameters.declare('engine_names', default=[], types=list)
    def define(self):        # iterate over a number of engines, or a list of engine names        num_engines = self.parameters['num_engines']        engine_names = self.parameters['num_engines']        r = range(num_engines)        if len(engine_names) > 0:          r = engine_names
        # add specified number of engines        for i in r:            # suppress promotions because all engines will have an            # output with the same name            self.add(EngineModel(),                name='engine_{}'.format(i),                promotes=[],            )
        # compute total thrust provided by engines        thrusts = []        for i in r:            # declare a variable for each thrust            local_name = 'thrust_{}'.format(i)            thrust = self.declare_variable(local_name)            # connect thrust from each engine to a locally defined            # thrust variable            self.connect(                'engine_{}.thrust'.format(i),                local_name,            )            # store each variable reference in a list so it doesn't get            # deleted when it goes out of scope            thrusts.append(thrust)
        # sum the thrusts using standard library function, sum        total_thrust = csdl.sum(*thrusts)        self.register_output('total_thrust', total_thrust)

note

All Python loops within a Model.define definition are compile time loops. That is, the loops are used to construct the mathematical specification procedurally within the CSDL compiler front end, and are not executed during simulation.