def eval(cls, *arg):
""" Called from sympy to evaluate the function """
if (not isinstance(arg[0], Variable)
and not isinstance(arg[0], Parameter)):
raise EquationError('not-a-variable', str(arg[0]),
'Must be a var or param')
if arg[0].model is None:
raise EquationError('no-model', arg[0].name,
'Variable must belong to a model')
return arg[0].model.get_at(arg[0], arg[1])
def _validate_equations(self):
""" Does some validation """
# Make sure that each variable has an equation
for variable in self.variables.values():
if variable.equation is None:
raise EquationError('under-specified', variable.name,
'variable does not have equation')
def eval(cls, *arg):
""" Called from sympy to evaluate the function """
if (not isinstance(arg[0], Variable)
and not isinstance(arg[0], Parameter)):
raise EquationError('d-arg-not-a-variable', str(arg[0]),
'The arg to d() must be a var or param')
return arg[0] - arg[0].model.get_at(arg[0], -1)
def get_at(self, name, iteration):
""" Implements the model get_at() """
# pylint: disable=no-self-use
if not iteration.is_number or not iteration.is_Number:
raise EquationError('test-not-a-number', '', '')
if iteration < 0:
return Symbol("_{0}__{1}".format(name, -iteration))
else:
return Symbol("_{0}_{1}".format(name, iteration))
def get_at(self, variable, iteration):
""" Returns the variable for a previous iteration.
The value for iter may be positive or negative:
If >= 0, absolute position
0 is the very first iteration. Note that
iterations are available only AFTER the
solver has returned success. Otherwise the
variable's default value is returned.
If < 0, relative position
-1 is the iteration previous to the current
iteration.
Arguments:
variable:
iteration:
Returns:
The value of the variable for that iteration.
"""
# Need to replace the iteration needed with a variable
# that represents the accessed variable
# for example, if are processing iteration 10
# then x[-1] -> _x__1
# _x__1 then gets added as a parameter
#
# For positive iterations, that's a static iteration
# x[5] -> _x_5
# _x_5 will get added as a parameter.
# If iteration 5 has not happened yet, the default value
# value will be returned.
#
# Before solving, the appropriate values will be set in the
# parameters.
#
iter_value = sympify(iteration)
if not iter_value.is_number or not iter_value.is_Number:
raise EquationError('iteration-not-a-number', str(iter_value),
'iteration value must be a number')
iter_value = int(iter_value)
if iter_value < 0:
iter_name = "_{0}__{1}".format(str(variable), -iter_value)
else:
iter_name = "_{0}_{1}".format(str(variable), iter_value)
if iter_name not in self._private_parameters:
param = SeriesParameter(iter_name,
variable=variable,
iteration=iter_value,
default=variable.default)
self._private_parameters[iter_name] = param
_add_param_to_context(self._local_context, param)
self._need_function_update = True
return self._private_parameters[iter_name]