Matrix arithmetic operations

faer matrices implement most of the arithmetic operators, so two matrices can be added simply by writing &a + &b, the result of the expression is a faer::Mat, which allows simple chaining of operations (e.g. (&a + faer::scale(3.0) * &b) * &c), although at the cost of allocating temporary matrices.

Temporary allocations can be avoided by using the zipped! api:

use faer::{Mat, zipped, unzipped};

let a = Mat::<f64>::zeros(4, 3);
let b = Mat::<f64>::zeros(4, 3);
let mut c = Mat::<f64>::zeros(4, 3);

// Sums `a` and `b` and stores the result in `c`.
zipped!(&mut c, &a, &b).for_each(|unzipped!(c, a, b)| *c = *a + *b);

// Sums `a`, `b` and `c` into a new matrix `d`.
let d = zipped!(&mut c, &a, &b).map(|unzipped!(c, a, b)| *a + *b + *c);

For matrix multiplication, the non-allocating api in-place is provided in the faer::linalg::matmul module.

use faer::{Mat, Parallelism};
use faer::linalg::matmul::matmul;

let a = Mat::<f64>::zeros(4, 3);
let b = Mat::<f64>::zeros(3, 5);

let mut c = Mat::<f64>::zeros(4, 5);

// Computes `faer::scale(3.0) * &a * &b` and stores the result in `c`.
matmul(c.as_mut(), a.as_ref(), b.as_ref(), None, 3.0, Parallelism::None);

// Computes `faer::scale(3.0) * &a * &b + 5.0 * &c` and stores the result in `c`.
matmul(c.as_mut(), a.as_ref(), b.as_ref(), Some(5.0), 3.0, Parallelism::None);