Outer product  #1148

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1. jturner314 commented on Jan 22, 2022

   

   jturner314

   on Jan 22, 2022

   Member

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   A useful generalization is numpy.ufunc.outer. That would be more work to implement efficiently, though, because we couldn't reuse the matrix multiplication implementation.
2. vladfaust commented on Jul 25, 2025

   

   vladfaust

   on Jul 25, 2025

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   For 2 dimensional arrays:

   pub fn outer_product2(a: &ArrayView2<f32>, b: &ArrayView2<f32>) -> Array4<f32> {
       let (m, n) = a.dim();
       let (p, q) = b.dim();
   
       let a_reshaped = a.to_shape((m, n, 1, 1)).unwrap();
       let b_reshaped = b.to_shape((1, 1, p, q)).unwrap();
   
       let prod = &a_reshaped * &b_reshaped;
   
       prod.to_owned()
   }
   
   #[test]
   fn test_outer_product2() {
       // -6	10
       // -8	5
       let a = array![[-6., 10.], [-8., 5.]];
   
       // 7	-6
       // 0	-2
       let b = array![[7., -6.], [0., -2.]];
   
       // |-42 36|	|70 -60|
       // |0   12|	|0  -20|
       // -------- --------
       // |-56 48| |35 -30|
       // |0   16| |0  -10|
       let expected = array![
           [[[-42., 36.], [0., 12.]], [[70., -60.], [0., -20.]]],
           [[[-56., 48.], [0., 16.]], [[35., -30.], [0., -10.]]]
       ];
   
       let result = outer_product2(&a.view(), &b.view());
       assert_eq!(result, expected);
   
       // |-42 70| |36 -60|
       // |-56 35| |48 -30|
       // -------- --------
       // |0    0| |12 -20|
       // |0    0| |16 -10|
       let expected = array![
           [[[-42., 70.], [-56., 35.]], [[36., -60.], [48., -30.]]],
           [[[0., 0.], [0., 0.]], [[12., -20.], [16., -10.]]]
       ];
   
       let result = outer_product2(&b.view(), &a.view());
       assert_eq!(result, expected);
   }