sphrs version 0.2.0 blog post

media/website/content/blog/sphrs_v0.2.0.md

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+title = "sphrs 0.2.0 released"
+description = ""
+date = 2023-01-15T00:00:00+00:00
+updated = 2023-01-15T00:00:00+00:00
+draft = false
+template = "blog/page.html"
+
+[taxonomies]
+authors = ["Stefan Kroboth"]
+
+[extra]
+math = true
++++
+
+This post announces the release of version 0.2.0 of <b>sphrs</b>, a spherical harmonics and solid harmonics library for Rust.
+
+## Introduction to sphrs
+
+The crate computes
+
+* real and complex spherical harmonics
+* real and complex regular solid harmonics
+* real and complex irregular solid harmonics
+
+using Cartesian and polar coordinates. 
+
+Here is a small example to illustrate the API which computes the real valued spherical harmonic of degree \\(l=2\\) and order \\(m=1\\) at Cartesian position \\((x, y, z) = (1.0, 0.2, 1.4)\\):
+
+```rust
+use sphrs::{Coordinates, RealSH, SHEval};
+
+// l = 2
+let degree = 2;
+// m = 1
+let order = 1;
+
+// Define the position where the SH will be evaluated at
+// in Cartesian coordinates
+let p = Coordinates::cartesian(1.0, 0.2, 1.4);
+
+// Compute the real-valued SH value at `p` for l = 2, m = 1
+let computed_sh = RealSH::Spherical.eval(degree, order, &p);
+
+println!("SH ({}, {}): {:?}", degree, order, computed_sh);
+```
+
+The library also provides the type `HarmonicsSet` which computes all harmonics up to a given order and returns them in a `Vec`:
+
+```rust
+use sphrs::{ComplexSH, Coordinates, HarmonicsSet};
+
+// l = 3
+let degree = 3;
+
+// Create the harmonics set (in this case for complex SH)
+let sh = HarmonicsSet::new(degree, ComplexSH::Spherical);
+
+// Position in spherical coordinates where the set is evaluated at
+let p = Coordinates::spherical(1.0, 0.8, 0.4);
+
+// Evaluate. Returns a `Vec<f64>`
+let set = sh.eval(&p);
+
+println!("SH up to degree {}: {:?}", degree, set);
+
+// The individual SHs can also be multiplied with coefficients
+// Note: `coeff` must have the same length as the number of SH.
+let coeff = vec![2.0; sh.num_sh()];
+let set = sh.eval_with_coefficients(&p, coeff.as_slice());
+
+println!("SH up to degree {}: {:?}", degree, set);
+```
+
+More details on how to use sphrs can be found in the [API documentation](https://docs.rs/sphrs/latest/sphrs/). 
+
+Harmonics up to third order are implemented according to their respective formulas in order to achieve good performance. 
+For higher orders, a recursive implementation is used.
+
+## Version 0.2.0
+
+The new version follows more than a year after the previous version 0.1.3 and comes with a couple of changes.
+Most of those changes concern the project structure and the CI; however some are user-facing and breaking changes:
+
+* Updated dependencies `num` (v0.4), `num-complex` (v0.4) and `num-traits` (v0.2)
+* Updated to Rust Edition 2021
+* Improved documentation
+* Every `SH` in function names was changed to `sh`
+* `RealSHType` and `ComplexSHType` lost their `Type` prefix and are now just `RealSH` and `ComplexSH`
+* Functions which accepted `&dyn SHCoordinates` now accept `&impl SHCoordinates` instead
+* The modules `coords` and `sh` are not `pub` anymore, all relevant types are re-exported at the crate root
+* Removed automatic conversion of inputs to the type of the output when creating `Coordinates`, since this required users to provide the desired output type as type hints:
+
+```rust
+// Version 0.1.3 (required a type hint)
+// Still compiles in 0.2.0
+let p: Coordinates<f64> = Coordinates::spherical(1.0, 0.8, 0.4);
+
+// Version 0.2.0 (does not require a type hint)
+// The `T` of `Coordinates<T>` will be equal to the type of the input arguments
+let p = Coordinates::spherical(1.0, 0.8, 0.4);
+```
+
+* The generics of `HarmonicsSet` were also changed such that type hints are not necessary anymore. In fact, the type hints needed with 0.1.3 will break compilation with 0.2.0:
+
+```rust
+// Version 0.1.3 (required a type hint)
+// This will *not* compile in 0.2.0
+let sh: HarmonicsSet<f64, _, _> = HarmonicsSet::new(degree, RealSHType::Spherical);
+
+// Version 0.2.0 (does not require a type hint)
+let sh = HarmonicsSet::new(degree, RealSHType::Spherical);
+```
+
+## Acknowledgements
+
+The implementation is inspired by Google's [spherical-harmonics](https://github.com/google/spherical-harmonics) library and follows the math outlined in [this document](https://theory.cpe.ku.ac.th/~pramook/files/spherical-harmonic-lighting.pdf).
+
+## Future steps
+
+In the future this crate will hopefully see an increase in test coverage and potentially a Python wrapper. 
+If you have any ideas for further development or if you even want to contribute, feel free to [open an issue](https://github.com/argmin-rs/sphrs/issues).
+
+
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