Fix unstable output of periodic sequence due to precision error.

[shunping]

A fix following #35300.

See the explanation below (copied from the inline comments):

In ImpulseSeqGenRestrictionProvider, the total number of counts (i.e. total_outputs) is computed by ceil((end - start) / interval) (

beam/sdks/python/apache_beam/transforms/periodicsequence.py

Line 45 in facdc4e

total_outputs=math.ceil((end-start) /interval)

), where end is start + duration (

beam/sdks/python/apache_beam/ml/ts/util.py

Line 172 in facdc4e

stop=start+min(self._duration, self._max_duration)

).

Due to precision error of arithmetic operations, even if duration is set to len(self._data) * interval, (end - start) / interval could be a little bit smaller or bigger than len(self._data).

In case of being bigger, total_outputs would be len(self._data) + 1, as the ceil() operation is used, which is NOT what we want.

Assuming that the precision error is no bigger than 1%, by subtracting a small amount, we ensure that the result after ceil() is stable even if a certain degree of precision error is present.

[shunping]

@claudevdm, could you please review this one too since you did the previous one and have some context? Thanks a lot!

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[shunping]

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[shunping]

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[shunping]

Thanks @claudevdm!