Matrix A (3 rows, 3 cols)      Matrix B (3 rows, 3 cols)

  ┌─────┬─────┬─────┐           ┌─────┬─────┬─────┐
  │ a11 │ a12 │ a13 │           │ b11 │ b12 │ b13 │
  ├─────┼─────┼─────┤           ├─────┼─────┼─────┤
  │ a21 │ a22 │ a23 │           │ b21 │ b22 │ b23 │
  ├─────┼─────┼─────┤           ├─────┼─────┼─────┤
  │ a31 │ a32 │ a33 │           │ b31 │ b32 │ b33 │
  └─────┴─────┴─────┘           └─────┴─────┴─────┘

Position (row 1, col 1) in A only ever combines with position (row 1, col 1) in B.
Position (row 2, col 3) in A only ever combines with position (row 2, col 3) in B.
And so on, for every single position.

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