Atomic Types

ANDES contains three types of atom classes for building DAE models. These types are parameter, variable and service.

Value Provider

Before addressing specific atom classes, the terminology v-provider, and e-provider are discussed. A value provider class (or v-provider for short) references any class with a member attribute named v, which should be a list or a 1-dimensional array of values. For example, all parameter classes are v-providers, since a parameter class should provide values for that parameter.

Note

In fact, all types of atom classes are v-providers, meaning that an instance of an atom class must contain values.

The values in the v attribute of a particular instance are values that will substitute the instance for computation. If in a model, one has a parameter

self.v0 = NumParam()
self.b = NumParam()

# where self.v0.v = np.array([1., 1.05, 1.1]
#   and self.b.v  = np.array([10., 10., 10.]

Later, this parameter is used in an equation, such as

self.v = ExtAlgeb(model='Bus', src='v',
                  indexer=self.bus,
                  e_str='v0 **2 * b')

While computing v0 ** 2 * b, v0 and b will be substituted with the values in self.v0.v and self.b.v.

Sharing this interface v allows interoperability among parameters and variables and services. In the above example, if one defines v0 as a ConstService instance, such as

self.v0 = ConstService(v_str='1.0')

Calculations will still work without modification.

Equation Provider

Similarly, an equation provider class (or e-provider) references any class with a member attribute named e, which should be a 1-dimensional array of values. The values in the e array are the results from the equation and will be summed to the numerical DAE at the addresses specified by the attribute a.

Note

Currently, only variables are e-provider types.

If a model has an external variable that links to Bus.v (voltage), such as

self.v = ExtAlgeb(model='Bus', src='v',
                  indexer=self.bus,
                  e_str='v0 **2 * b')

The addresses of the corresponding voltage variables will be retrieved into self.v.a, and the equation evaluation results will be stored in self.v.e