generics - 如何将 ndarray 中的元素与 Rust 中的泛型相乘？

Question

我有一个 ndarray 二维数组，我试图用相同的数字乘以一行，如 here 所述.

当我使用 f64 的二维数组时它工作正常，但我希望它对所有类型的 float 都是通用的。这就是我使用 num-traits 中的 Float 的原因。但是，它不再编译。

use ndarray::{Array2, Axis};

fn gauss(pivot: [usize; 2], table: &mut Array2<f64>) {
    for i in 0..table.len_of(Axis(0)) {
        if i != pivot[0] {
            let pivot_n = table[pivot];
            let make_zero = table[[i, pivot[1]]];
            let mut row_pivot = table.row(pivot[0]).to_owned();
            let mut row_make_zero = table.row_mut(i);
            row_make_zero *= pivot_n;
            row_pivot *= -make_zero;
            row_make_zero += &row_pivot;
        }
    }
}

use num::Float;
use std::ops::MulAssign;

fn gauss_2<T: Float + MulAssign>(pivot: [usize; 2], table: &mut Array2<T>) {
    for i in 0..table.len_of(Axis(0)) {
        if i != pivot[0] {
            let pivot_n = table[pivot];
            let make_zero = table[[i, pivot[1]]];
            let mut row_pivot = table.row(pivot[0]).to_owned();
            let mut row_make_zero = table.row_mut(i);
            row_make_zero *= pivot_n;
            row_pivot *= -make_zero;
            row_make_zero += &row_pivot;
        }
    }
}

它显示的错误是:

error[E0308]: mismatched types
  --> src/lib.rs:27:30
   |
27 |             row_make_zero *= pivot_n;
   |                              ^^^^^^^ expected reference, found type parameter
   |
   = note: expected type `&ndarray::ArrayBase<_, _>`
              found type `T`

error[E0308]: mismatched types
  --> src/lib.rs:28:26
   |
28 |             row_pivot *= -make_zero;
   |                          ^^^^^^^^^^ expected reference, found type parameter
   |
   = note: expected type `&ndarray::ArrayBase<_, _>`
              found type `T`

error[E0368]: binary assignment operation `+=` cannot be applied to type `ndarray::ArrayBase<ndarray::ViewRepr<&mut T>, ndarray::dimension::dim::Dim<[usize; 1]>>`
  --> src/lib.rs:29:13
   |
29 |             row_make_zero += &row_pivot;
   |             -------------^^^^^^^^^^^^^^
   |             |
   |             cannot use `+=` on type `ndarray::ArrayBase<ndarray::ViewRepr<&mut T>, ndarray::dimension::dim::Dim<[usize; 1]>>`
   |
   = note: an implementation of `std::ops::AddAssign` might be missing for `ndarray::ArrayBase<ndarray::ViewRepr<&mut T>, ndarray::dimension::dim::Dim<[usize; 1]>>`

Answer 1

如果你想在那种操作中使用T，你必须为T要求ndarray::ScalarOperand。这是固定的代码:

use ndarray::{Array2, ScalarOperand};
use num::Float;
use std::ops::{AddAssign, MulAssign};

fn gauss<T>(pivot: [usize; 2], table: &mut Array2<T>)
where
    T: Float + MulAssign + AddAssign + ScalarOperand,
{
    for i in 0..table.len_of(Axis(0)) {
        if i != pivot[0] {
            // Aplicar GAUSS a la fila
            let pivot_n = table[pivot];
            let make_zero = table[[i, pivot[1]]];
            // Multiplicar la fila de make_zero por pivot_n
            let mut row_pivot = table.row(pivot[0]).to_owned();
            let mut row_make_zero = table.row_mut(i);
            row_make_zero *= pivot_n;
            row_pivot *= -make_zero;
            row_make_zero += &row_pivot;
        }
    }
}