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Calculate Relative Strength Index (RSI) algorithm - #13888

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toonyyy wants to merge 1 commit into
TheAlgorithms:masterfrom
toonyyy:relative_strength_index
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toonyyy wants to merge 1 commit into
TheAlgorithms:masterfrom
toonyyy:relative_strength_index

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@toonyyy

@toonyyy toonyyy commented Nov 9, 2025

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Describe your change:

Implemented the Relative Strength Index (RSI) algorithm, which analyses an array of stock prices to indicate whether a stock is overbought or oversold.

  • Add an algorithm?
  • Fix a bug or typo in an existing algorithm?
  • Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
  • Documentation change?

Checklist:

  • I have read CONTRIBUTING.md.
  • This pull request is all my own work -- I have not plagiarized.
  • I know that pull requests will not be merged if they fail the automated tests.
  • This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
  • All new Python files are placed inside an existing directory.
  • All filenames are in all lowercase characters with no spaces or dashes.
  • All functions and variable names follow Python naming conventions.
  • All function parameters and return values are annotated with Python type hints.
  • All functions have doctests that pass the automated testing.
  • All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
  • If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

@priya-sundaram-dev priya-sundaram-dev left a comment

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Thanks @toonyyy — the Wilder-smoothing RSI, type hints and doctest are all good. A couple of minor fixes:

  1. Typo in the first docstring line: "stciks prices" -> "stock prices".
  2. The function returns len(price_changes) values (one per price change), so the output is offset by one from stock_prices. A one-line note in the docstring clarifying the alignment (the first non-None value corresponds to the (window_size + 1)-th price) would save readers some head-scratching.
  3. Consider adding if __name__ == "__main__": import doctest; doctest.testmod() alongside the demo so the doctest runs locally, matching the repo convention.

Numerically it looks correct — nice work.

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2 participants