Defining a quantity

Import Quantity from the ansys.units package and instantiate a Quantity object, providing a numerical value and a unit string:

from ansys.units import Quantity

meter = Quantity(value=1, units="m")

You can also provide a Unit object (rather than a unit string) as a construction argument. Alternatively, you can instantiate a Quantity object by multiplying a Unit object by a value:

from ansys.units import Quantity, UnitRegistry

ureg = UnitRegistry()

meter = Quantity(value=1, units=ureg.m)
meter = 1 * ureg.m

With NumPy installed, you can instantiate a Quantity using either a list of floats or a NumPy array:

from ansys.units import Quantity
import numpy as np

length_array_quantity = Quantity(value=[1.0, 6.0, 7.0], units="m")
length_array_quantity[1]  # Quantity (6.0, "m")
time = Quantity(value=2, units="s")
speed = length_array_quantity / time
speed  # Quantity ([0.5 3. 3.5], "m s^-1")

All Quantity objects work intuitively with arithmetic operators:

from ansys.units import Quantity

meter = Quantity(value=1, units="m")

m_ml = meter * 2  # (2.0, "m")
m_dv = meter / 2  # (0.5, "m")
m_sq = meter**2  # (1.0, "m^2")

Additions and subtractions involving Quantity objects retain the units of the first operand:

from ansys.units import Quantity

meter = Quantity(value=1, units="m")
foot = Quantity(value=1, units="ft")

meter + foot  # Quantity (1.3048, "m")
foot + meter  # Quantity (4.2808398950131235, "ft")

This formula defines the conversion of Quantity objects between different units:

\[value_{\text{new}} = \frac{value_{\text{si}}}{f_{\text{new}}} - c_{\text{new}}\]

where \(f_{new}\) is a scaling factor and \(c_{new}\) is an offset to convert from SI units to the requested units.

To define a new unit system or create custom quantities, you can manually update the cfg.yaml file with your desired settings. Once saved, these changes are reflected the next time the ansys.units package is initialized.