quantity 0.4.0

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

[![crate](https://img.shields.io/crates/v/quantity.svg)](https://crates.io/crates/quantity)
[![documentation](https://docs.rs/quantity/badge.svg)](https://docs.rs/quantity)
[![documentation](https://img.shields.io/badge/docs-github--pages-blue)](https://itt-ustutt.github.io/quantity/index.html)
[![PyPI version](https://badge.fury.io/py/si_units.svg)](https://badge.fury.io/py/si_units)

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](https://github.com/rust-ndarray/ndarray) crate, where all entries share the same unit.

## Installation and Usage

### Rust

Add this to your `Cargo.toml`:

```
[dependencies]
quantity = "0.4"
```

## Python package

Python bindings for the SI functionalities are published under the name [si-units](https://pypi.org/project/si-units/) on PyPI.

## Examples

Calculate pressure of an ideal gas.

```rust
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.

```rust
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.

```rust
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](https://docs.rs/quantity).

For the python documentation, see [here](https://itt-ustutt.github.io/quantity/index.html).

## Development

To build the project including the bindings to python, we use [maturin](https://github.com/PyO3/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
```