Add EPSILON0 and KE as additional constants (#113)

Author: prehner

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added implementations for trigonometric funtions for `Angle<T>` with `T: DualNum<f64>` when the `num-dual` feature is active. [#105](https://github.com/itt-ustutt/quantity/pull/105)
 - Added `ATM` and `POISE` as additional units for pressure and viscosity.
+- Added `EPSILON0` and `KE` as additional constants. [#113](https://github.com/itt-ustutt/quantity/pull/113)
 
 ## [0.13.0] - 2026-01-06
 ### Changed

si-units/CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added `ATM` and `POISE` as additional units for pressure and viscosity.
 - Added `sum` for `SIObject`s that can be summed. [#111](https://github.com/itt-ustutt/quantity/pull/111)
+- Added `EPSILON0` and `KE` as additional constants. [#113](https://github.com/itt-ustutt/quantity/pull/113)
 
 ### Fixed
 - Fixed the String representation of non-scalar mass quantities. [#111](https://github.com/itt-ustutt/quantity/pull/111)

si-units/docs/derived.md

@@ -47,6 +47,8 @@ of quantities is unique, they do not appear in formatted outputs.
 | -------- | ---------------------- | ------------------------- | ------------------------------------------------------------------- |
 | G        | Gravitational constant | $G$                       | $6.6743\times 10^{-11}~\frac{\text{m}^3}{\text{kg}\cdot\text{s}^2}$ |
 | RGAS     | Ideal gas constant     | $R=N_\text{Av}k_\text{B}$ | $8.31446261815324~\frac{\text{J}}{\text{mol}\cdot\text{K}}$         |
+| EPSILON0 | Electric constant      | $\varepsilon_0$           | $8.8541878188e-12~\frac{\text{F}}{\text{m}}$                        |
+| KE       | Coulomb constant       | $k_\text{e} = \frac{1}{4\pi\varepsilon_0}$ | $8987551786.1708~\frac{\text{m}}{\text{F}}$        |
 
 ### Example
 

si-units/src/lib.rs

@@ -7,6 +7,7 @@ use pyo3::exceptions::PyRuntimeError;
 use pyo3::prelude::*;
 use pyo3::types::{PyFloat, PyNotImplemented};
 use pyo3::{PyErr, PyTypeInfo};
+use std::f64::consts::FRAC_1_PI;
 use thiserror::Error;
 
 mod si_unit;
@@ -537,6 +538,13 @@ pub fn _core(m: &Bound<'_, PyModule>) -> PyResult<()> {
     add_constant(m, "G", 6.6743e-11, SIUnit([3, -1, -2, 0, 0, 0, 0]))?;
     let rgas = 1.380649e-23 * 6.02214076e23;
     add_constant(m, "RGAS", rgas, _JOULE_PER_MOL_AND_KELVIN)?;
+    add_constant(m, "EPSILON0", 8.8541878188e-12, _FARAD / _METER)?;
+    add_constant(
+        m,
+        "KE",
+        FRAC_1_PI / (4.0 * 8.8541878188e-12),
+        _METER / _FARAD,
+    )?;
 
     m.add("QUECTO", QUECTO)?;
     m.add("RONTO", RONTO)?;

si-units/src/si_units/__init__.py

@@ -69,6 +69,8 @@
     MINUTE,
     G,
     RGAS,
+    EPSILON0,
+    KE,
     QUECTO,
     RONTO,
     YOCTO,
@@ -147,6 +149,8 @@
     "MINUTE",
     "G",
     "RGAS",
+    "EPSILON0",
+    "KE",
     "QUECTO",
     "RONTO",
     "YOCTO",

si-units/src/si_units/_core.pyi

@@ -254,6 +254,8 @@ LITER: Final[SIObject]
 MINUTE: Final[SIObject]
 G: Final[SIObject]
 RGAS: Final[SIObject]
+EPSILON0: Final[SIObject]
+KE: Final[SIObject]
 QUECTO: Final[float]
 RONTO: Final[float]
 YOCTO: Final[float]

src/lib.rs

@@ -68,6 +68,8 @@
 //! -|-|-|-
 //! [G] | Gravitational constant | $G$ | $6.6743\\times 10^{-11}\\,\\frac{\text{m}^3}{\text{kg}\cdot\text{s}^2}$
 //! [RGAS] | Ideal gas constant | $R=N_\text{Av}k_\text{B}$ | $8.31446261815324\\,\\frac{\text{J}}{\text{mol}\\cdot\text{K}}$
+//! [EPSILON0] | Electric constant | $\varepsilon_0$ | $8.8541878188e-12~\frac{\text{F}}{\text{m}}$
+//! [KE] | Coulomb constant | $k_\text{e} = \frac{1}{4\pi\varepsilon_0}$ | $8987551786.1708~\frac{\text{m}}{\text{F}}$
 //!
 //! ## Prefixes
 //!
@@ -143,6 +145,7 @@
 #![warn(clippy::all)]
 #[cfg(feature = "ndarray")]
 use ndarray::{Array, ArrayBase, Data, Dimension};
+use std::f64::consts::FRAC_1_PI;
 use std::marker::PhantomData;
 use std::ops::{Add, Deref, Div, Mul, Neg, Sub};
 
@@ -556,6 +559,12 @@ pub const CLIGHT: Velocity = Quantity(299792458.0, PhantomData);
 pub const KCD: Quantity<f64, SIUnit<-2, -1, 3, 0, 0, 0, 1>> = Quantity(683.0, PhantomData);
 /// Gravitational constant $\\left(G=6.6743\\times 10^{-11}\\,\\frac{\text{m}^3}{\text{kg}\cdot\text{s}^2}\\right)$
 pub const G: Quantity<f64, SIUnit<-2, 3, -1, 0, 0, 0, 0>> = Quantity(6.6743e-11, PhantomData);
+/// Electric constant $\\left(\\varepsilon_0=8.8541878188\times 10^{-12}\\,\\frac{\text{F}}{\text{m}}\\right)$
+pub const EPSILON0: Quantity<f64, SIUnit<4, -3, -1, 2, 0, 0, 0>> =
+    Quantity(8.8541878188e-12, PhantomData);
+/// Coulomb constant $\\left(k_\text{e}=\frac{1}{4\pi\varepsilon_0}=8987551786.1708\\,\\frac{\text{m}}{\text{F}}\\right)$
+pub const KE: Quantity<f64, SIUnit<-4, 3, 1, -2, 0, 0, 0>> =
+    Quantity(FRAC_1_PI / (4.0 * 8.8541878188e-12), PhantomData);
 
 /// Prefix quecto $\\left(\text{q}=10^{-30}\\right)$
 pub const QUECTO: f64 = 1e-30;