Python / NumPy · How axes stretch

Broadcasting shapes

Pick two ndarray shapes and see whether NumPy can align them — and what the result looks like.

Array A

Array B

Result shape

(3, 4)

Align shapes on the right. A 1 stretches; a missing leading axis is a 1. Two disagreeing non-1 axes refuse. That is the whole rule.

Right-aligned axes

axis	A	B	out
0	3	1	3
1	4	4	4

A trailing axis

B trailing axis

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Broadcasting shapes

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