## quantity

Representation of quantites, i.e. of unit valued scalars and arrays.

### 14 unstable releases(6 breaking)

 0.7.0 Oct 15, 2023 Jan 20, 2023 Jun 8, 2022 Mar 9, 2022 Jul 26, 2021

#127 in Data structures

Used in 7 crates

MIT/Apache

120KB
2.5K SLoC

# quantity

Representation of quantities, 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

### Rust

Add this to your `Cargo.toml`:

``````[dependencies]
quantity = "0.6"
``````

## Python package

Python bindings for the SI functionalities are published under the name si-units on PyPI.

## Examples

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 -m si-units/Cargo.toml
``````

To build the python wheels, use

``````maturin build --release -m si-units/Cargo.toml
``````

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

``````cd si-units/docs
make html
``````

To run the doctests, from the root directory, type

``````cd si-units/docs
make doctest
``````

~4–12MB
~120K SLoC