add Indicator.unstablePeriod

[nimo23]

Fixes #.

Changes proposed in this pull request:

• add Indicator#getUnstablePeriod()

• added an entry with related ticket number(s) to the unreleased section of CHANGES.md

The main purpose of the PR is:

Actually, the user must know which value to set for Strategy#unstablePeriod. However, this is not easy to know, because the user is not always aware of the technical details of the indicators (e.g. SARIndicator needs at least 200 bars before the values can be calculated correctly, other indicators needs at least its barCount, etc.). It's better to have this information (about the unstablePeriod of an indicator) implemented and documented within each Indicator. The implementor of the indicator must provide this information within the source code of the indicator. With this, the user can retrieve this information (by Indicator#getUnstablePeriod()) for various use cases.

[nimo23]

Maybe we should also rename getUnstablePeriod() to getUnstableBars(), because we have bars and not periods, or?

[team172011]

I am still unsure about this enhancement, especially for indicators that have an unstable period, it should be up to the user to decide when the data of the indicator is useful. For example a user with 190 bars would like to use the SARIndicator in his strategy anyway.

Furthermore just adding the getUnstablePeriod() without any usages does not change anything nor? If introduced this concept must also be implemented in the BarSeriesManager where the unstablePeriod will be checked for each index

[nimo23]

I am still unsure about this enhancement, especially for indicators that have an unstable period, it should be up to the user to decide when the data of the indicator is useful.

I thought it should be up to the indicator (and not the user) when the indicator's data is correct. I also thought that if an indicator needs a "warm-up" period (=unstable period), then it is a fixed value that should at least be "documented" (= in the form of getUnstablePeriod() ) within our indicator implementations.

Furthermore just adding the getUnstablePeriod() without any usages does not change anything nor?

Yes, this PR is only about putting getUnstablePeriod() within our indicators, nothing more. The user can use this method for its use cases..

If introduced this concept must also be implemented in the BarSeriesManager where the unstablePeriod will be checked for each index

Yes good idea. We could do this in a new PR after this has been merged (as I also explained in #919 (comment)). But the intention of this PR is only to draw attention to the fact that indicators can have an unstable period and the user can get this automatically by calling a method (=getUnstablePeriod()). Without this method, the user does not know when the calculated indicator value is really correct and usable.

[nimo23]

Another thing: should we call it getUnstablePeriod() or getUnstableBars()? Which name is more appropriate?

[team172011]

Another thing: should we call it getUnstablePeriod() or getUnstableBars()? Which name is more appropriate?

I would prefer getUnstableBars()

[nimo23]

Replaced by #944

[hhashim1]

Any updates/ETA on this?

[nimo23]

This PR is replaced by #944 (which is already merged). The issue #947 is the next step, feel free to share your suggestions in #947.