Why example of angle encoding is multiplying angles by 2 ?

[acastellane]

URL to the relevant course

https://quantum.cloud.ibm.com/learning/en/courses/quantum-machine-learning/data-encoding#check-your-understanding-2

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• typo
• code bug
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Solution provides for example: qc.ry(2 * math.pi / 4, 1)
Why do we mulltiply by 2 ?
I would expect qc.ry(pi / 4, 1) as in the previous example on 1 qbit.
Thanks for checking.

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[acastellane]

If we look at the next example (with 12 values, the largest of which is 9) , we normalize to 2pi. So we might need to multiply by 4 to have the max value being 2pi.
In any case, I would recommend we detail these steps.

[christopherporter1]

Alexandre CASTELLANE (@acastellane) Thank you! Excellent catch. I can't tell right now if it is an editing mistake in showing the "2x" argument at all, or if there was meant to be a line pointing out that some literature may use the convention with "theta" as the argument of the sine/cosine rather than as the argument of the RY gate. Either way, I have linked a PR to make it consistent. Many thanks!