einsum-derive
===============
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Proc-macro based einsum implementation for [ndarray](https://crates.io/crates/ndarray) crate

```rust
use ndarray::array;
use einsum_derive::einsum;

let a = array![
  [1.0, 2.0],
  [3.0, 4.0]
];
let b = array![
  [1.0, 2.0],
  [3.0, 4.0]
];
let c = einsum!("ij,jk->ik", a, b);
assert_eq!(c, array![
  [6.0, 8.0],
  [12.0, 16.0]
]);
```

This proc-macro wil compile the input subscripts `"ij,jk->ik"`
to generate Rust code executing corresponding operation.

Status / Roadmap
-----------------
- [x] [Optimal contraction by memorizing partial summation to reduce computation order.](https://github.com/termoshtt/einsum-derive/pull/18)
  - For example, three matrix multiplication `ij,jk,kl->il` is factorized into
    two successive einsum `ij,jk->ik` and `ik,kl->il`.
- [ ] [Call BLAS routines if possible](https://github.com/termoshtt/einsum-derive/issues/22)
- [ ] [Ellipsis `...` support](https://github.com/termoshtt/einsum-derive/issues/7)

Architecture
-------------
- [einsum-derive](https://termoshtt.github.io/einsum-derive/doc/einsum_derive/index.html)
  crate is proc-macro crate to provide above `einsum!` macro.
- [einsum-codegen](https://termoshtt.github.io/einsum-derive/doc/einsum_codegen/index.html)
  crate implements parser for the einsum subscripts like `ij,jk->ik` and generates Rust code.

Links
------
- [numpy.einsum](https://numpy.org/doc/stable/reference/generated/numpy.einsum.html) is well-known einsum implementation in Python.
- [opt_einsum](https://optimized-einsum.readthedocs.io/en/stable/) is an implementation for optimizing einsum computation for NumPy and other linear algebra packages.
- [oracleofnj/einsum](https://github.com/oracleofnj/einsum) is a runtime-based implementation of einsum for rust-ndarray

License
--------

© 2022 Toshiki Teramura (@termoshtt)

This project is licensed under either of

- Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or https://www.apache.org/licenses/LICENSE-2.0)
- MIT license ([LICENSE-MIT](LICENSE-MIT) or https://opensource.org/licenses/MIT)

at your option.