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[Feature request] `ArrayRef<A, Ix2>.dot()` for axis greater than `Ix2`

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@EbrahimEldesoky 已經在處理了。

開始於 2026年7月5日。

  • #1602 來自 @EbrahimEldesoky —— 未關閉

評估

難度
4/5
預估耗時
3-5 天
新手友好度
45/100
Issue 類型
功能
描述清晰度
基本清楚
活躍度
停滯
技術堆疊
rust
領域
data

研究方向

Start from the ndarray dot() entry point and inspect how dimensions are currently constrained. Compare the requested behavior with the provided Ix3-by-Ix2 example, then verify that higher-rank left-hand arrays produce the expected NumPy-compatible shape while preserving existing Ix2 behavior.

由索引模型根據 Issue 內容生成。

描述

enhancement question

In NumPy, the left-hand side of a matrix multiplication can have as many axes as desired, as long as it has more than 2 axes and the last axis's dimension matches that of the 0th axis of the right-hand side, e.g.:

import numpy as np
x = np.random.random((3, 2, 5, 9, 12))
y = np.random.random((12, 13))
(x @ y).shape

# (3, 2, 5, 9, 13)

In ndarray, you can't do this directly:

// Doesn't compile:
use ndarray::prelude::*;
use ndarray_rand::RandomExt;
use ndarray_rand::rand_distr::Uniform;


fn main() {
    let x: Array<f64, Ix3> = Array::random(
        (12, 4, 3),
        Uniform::new(0., 1.).unwrap()
    );
    let y: Array<f64, Ix2> = Array::random(
        (3, 2),
        Uniform::new(0., 1.).unwrap()
    );
    let x_y = x.dot(&y);
    println!("{}", x_y);
}
Compiler Output
$ cargo run
   Compiling playground v0.1.0 (/home/connor/RustroverProjects/playground)
error[E0275]: overflow evaluating the requirement `&ArrayBase<_, _, _>: Not`
  --> src/main.rs:15:17
   |
15 |     let x_y = x.dot(&y);
   |                 ^^^
   |
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`playground`)
   = note: required for `&ArrayBase<_, _, _>` to implement `Not`
   = note: 127 redundant requirements hidden
   = note: required for `&ArrayBase<OwnedRepr<f64>, Dim<[usize; 3]>, f64>` to implement `Not`

For more information about this error, try `rustc --explain E0275`.
error: could not compile `playground` (bin "playground") due to 1 previous error

Emulating the behavior in the previous NumPy example requires a non-trivial amount of work, e.g. for x with 3 axes:

use ndarray::prelude::*;
use ndarray_rand::RandomExt;
use ndarray_rand::rand_distr::Uniform;


fn main() {
    let x: Array<f64, Ix3> = Array::random((12, 4, 3), Uniform::new(0., 1.).unwrap());
    let y = Array::random((3, 2), Uniform::new(0., 1.).unwrap());

    let (a, b, c) = (x.len_of(Axis(0)), x.len_of(Axis(1)), x.len_of(Axis(2)));
    let d = y.len_of(Axis(1));

    let x_y: Array3<f64> = x
        .to_shape((a * b, c)).unwrap()
        .dot(&y)
        .to_shape((a, b, d)).unwrap()
        .to_owned();
    println!("{:?}", x_y);
}

Therefore, I think it would be nice to have dot() be implemented for axis numbers greater than Ix2

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