Physical units as global variables for simple numerical propagation
Project description
physunits
Simple package with common physical unit definitions.
Installation
Add this package to your existing python environment with pip
pip install physunits
, or alternatively follow your distribution specific instructions.
Usage
An example usage of this package is:
>> from physunits import *
>> print(f"{1000 * cm / um:.2f} is how many microns there are in a thousand centimeters")
10000000.00 is how many microns there are in a thousand centimeters
The package tries to include only the most used unit prefixes, but you can generate other units, for example:
>> from physunits import *
>> minute = 60 * s
>> hour = 60 * minute
>> day = 24 * hour
>> print(f'There are approximately {365*day / hour} hours in a year.')
There are approximately 8760.0 hours in a year.
The unit prefixes act as simple globals. If only a subset of the supported units is desired, manually importing them as
from physunits import mm, nm, um
is good enough.
Another example where physunits may be useful is illustrated by the following script dealing with a voltage trace:
import numpy as np
import matplotlib.pyplot as plt
from physunits import *
f = 2.12*kHz
omega = 2*np.pi*f
t = np.linspace(-670*us, 410*us, 2**10)
my_voltage = (1.5*mV) * np.sin(omega*t)
# Now plot voltage in mV vs time in ms
plt.plot(t/ms, my_voltage/mV)
plt.xlabel(r't (ms)')
plt.ylabel(r'V (mV)')
plt.show()
which outputs the following plot:
Description
All units are referenced to the SI. This means that base, derived, freedom (imperial), and other units including prefixes are always relative to the SI base units. An example where this is manifest is that when imported, the unit kg
takes on the numerical value 1.0
, regardless of the prefix indicating the numerical factor of 1000
.
Unit | Supported |
---|---|
length | nm, um, mm, cm, m, km, inch, ft, yd |
time | ps, ns, us, ms, s |
mass | ng, ug, mg, g, kg, lb, oz |
temperature | nK, uK, mK, K |
angle* | deg, rad, mrad |
frequency | mHz, Hz, kHz, MHz, GHz, THz |
voltage | pV, nV, uV, mV, V, kV |
charge | C, mC, uC, nC |
current | nA, uA, mA, A |
resistance | ohm, mohm, kohm, Mohm |
capacitance | F, mF, uF, nF, pF |
inductance | H, mH, uH, nH |
energy** | mJ, J, kJ, meV, eV, keV, MeV, GeV, TeV |
power | nW, uW, mW, W, kW, MW |
pressure | mPa, Pa, kPa, MPa, atm, psi, Torr, mBar, Bar |
rel concentration | ppm, ppb |
If you want a unit to be supported, feel free to open an issue.
- We all know that if there was an SI unit for angles, it would be the radian, so in
physunits
, it takes the valuerad = 1.0
, and degrees are defined relative to it. This works nicely in all trig functions. Special thanks to chrisjbillington for pointing this out.
** While the electronvolt (eV
) is not a part of the SI, the SI recognizes its use. Furthermore, the latest SI redefinition fixed the value of the electron charge constant, effectively fixing the conversion between eV
and J
.
Contact and support
Please report, fork, test, contribute, or create an issue directly on the project's repository.
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