quantity

Representation of quantites, i.e. of unit valued scalars and arrays. Rust library with Python bindings.

As opposed to other implementations, this crate does not attempt to achieve compile time checks on units. It is written with flexibility in mind and is able to represent arbitrarily complex units. Additional to simple scalar quantities, it also provides utilities for vector valued quantities, based on the ndarray crate, where all entries share the same unit.

Installation and Usage

Python

You can install the python package either from pypi:

pip install quantity

of from source (you need a rust compiler for that):

pip install git+https://github.com/itt-ustutt/quantity

Rust

Add this to your Cargo.toml:

[dependencies]
quantity = "0.3"

Examples

Python

Calculate pressure of an ideal gas.

from quantity import *
temperature = 25.0 * CELSIUS
volume = 1.5 * METER**3
moles = 75.0 * MOL
pressure = moles * RGAS * temperature / volume
print(pressure) # 123.94785148011941 kPa

numpy functions can be used with quantities:

from quantity import *
import numpy as np
ms = np.array([2.0, 3.0, 4.0]) * METER
sqms = np.square(ms)
print(sqms) # [4, 9, 16] m²
print(np.sqrt(sqms)) # [2, 3, 4] m

Rust

Calculate pressure of an ideal gas.

let temperature = 25.0 * CELSIUS;
let volume = 1.5 * METER.powi(3);
let moles = 75.0 * MOL;
let pressure = moles * RGAS * temperature / volume;
println!("{:.5}", pressure);            // 123.94785 kPa

Calculate the gravitational pull of the moon on the earth.

let mass_earth = 5.9724e24 * KILOGRAM;
let mass_moon = 7.346e22 * KILOGRAM;
let distance = 383.398 * KILO * METER;
let force = G * mass_earth * mass_moon / distance.powi(2);
println!("{:.5e}", force);              // 1.99208e26 N

Calculate the pressure distribution in the atmosphere using the barometric formula.

let z = SIArray1::linspace(1.0 * METER, 70.0 * KILO * METER, 10)?;
let g = 9.81 * METER / SECOND.powi(2);
let m = 28.949 * GRAM / MOL;
let t = 10.0 * CELSIUS;
let p0 = BAR;
let pressure = p0 * (-&z * m * g).to_reduced(RGAS * t)?.mapv(f64::exp);
for i in 0..10 {
    println!("z = {:8.5}   p = {:9.5}", z.get(i), pressure.get(i));
}
// z =  1.00000  m   p =  99.98794 kPa
// z =  7.77867 km   p =  39.12796 kPa
// z = 15.55633 km   p =  15.31182 kPa
// z = 23.33400 km   p =   5.99192 kPa
// z = 31.11167 km   p =   2.34480 kPa
// z = 38.88933 km   p = 917.58301  Pa
// z = 46.66700 km   p = 359.07479  Pa
// z = 54.44467 km   p = 140.51557  Pa
// z = 62.22233 km   p =  54.98750  Pa
// z = 70.00000 km   p =  21.51808  Pa

Documentation

For the rust documentation, see here. For the python documentation, see here.

Development

To build the project including the bindings to python, we use maturin.

When developing, use

maturin develop --release --cargo-extra-args="--features python"

To build the python wheels, use

maturin build --release --cargo-extra-args="--features python"

To build the documentation you need sphinx and some additional packages. From the root directory, type

cd docs
make html

To run the doctests, from the root directory, type

cd docs
make doctest