def derive_unit(expr, name=None):
"""Derive SI-unit from an expression, omitting scale factors."""
from essm.variables import Variable
from essm.variables.utils import extract_variables
from sympy.physics.units import Dimension
from sympy.physics.units.dimensions import dimsys_SI
variables = extract_variables(expr)
for var1 in variables:
q1 = Quantity('q_' + str(var1))
q1.set_dimension(
Dimension(Quantity.get_dimensional_expr(var1.definition.unit)))
q1.set_scale_factor(var1.definition.unit)
expr = expr.xreplace({var1: q1})
dim = Dimension(Quantity.get_dimensional_expr(expr))
return functools.reduce(
operator.mul,
(SI_DIMENSIONS[d]**p
for d, p in dimsys_SI.get_dimensional_dependencies(dim).items()), 1)
def derive_baseunit(expr, name=None):
"""Derive SI base unit from an expression, omitting scale factors."""
from essm.variables import Variable
from essm.variables.utils import extract_variables
from sympy.physics.units import Dimension
from sympy.physics.units.systems.si import dimsys_SI
Variable.check_unit(expr) # check for dimensional consistency
variables = extract_variables(expr)
for var1 in variables:
q1 = Quantity('q_' + str(var1))
SI.set_quantity_dimension(
q1,
Dimension(
SI.get_dimensional_expr(derive_baseunit(
var1.definition.unit))))
SI.set_quantity_scale_factor(q1, var1.definition.unit)
expr = expr.xreplace({var1: q1})
dim = Dimension(Variable.get_dimensional_expr(expr))
return functools.reduce(
operator.mul,
(SI_BASE_DIMENSIONS[Symbol(d)]**p
for d, p in dimsys_SI.get_dimensional_dependencies(dim).items()), 1)
def test_variable_extraction():
"""Test extract variables from expression."""
expr = demo_fall.rhs
assert extract_variables(expr) == {demo_g, demo_fall.definition.t}