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feat(maths): add LU decomposition algorithm for matrix factorization#14697

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feat(maths): add LU decomposition algorithm for matrix factorization#14697
MD-Mushfiqur123 wants to merge 1 commit into
TheAlgorithms:masterfrom
MD-Mushfiqur123:add-lu-decomposition-v2

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Describe your change:

  • 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".

LU Decomposition Algorithm

Adds LU decomposition (Doolittle algorithm) to the maths module for matrix factorization and solving systems of linear equations.

What This Adds

A new maths/lu_decomposition.py file containing:

lu_decomposition(matrix)

Performs LU decomposition on a square matrix, returning (L, U) where:

  • L is a lower triangular matrix with ones on the diagonal
  • U is an upper triangular matrix
  • A = L * U

solve_with_lu(lower, upper, b)

Solves the system Ax = b using the LU decomposition, via:

  1. Forward substitution (L * y = b)
  2. Back substitution (U * x = y)

Features

  • Comprehensive docstrings with mathematical explanation
  • Full doctest coverage (10 tests, all passing)
  • Input validation (square matrix check, zero pivot detection)
  • Type hints for all parameters and return values
  • Demonstration code in __main__ block

Algorithm

Uses the Doolittle algorithm with O(n^3) time complexity for decomposition and O(n^2) for solving. More efficient than Gaussian elimination when solving multiple systems with the same coefficient matrix.

Testing

python -m doctest maths/lu_decomposition.py -v

All 10 doctests pass.

@algorithms-keeper algorithms-keeper Bot added the require descriptive names This PR needs descriptive function and/or variable names label May 18, 2026

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Click here to look at the relevant links ⬇️

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Python:

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Comment thread maths/lu_decomposition.py


def solve_with_lu(
lower: list[list[float]], upper: list[list[float]], b: list[float]

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Please provide descriptive name for the parameter: b

@algorithms-keeper algorithms-keeper Bot added awaiting reviews This PR is ready to be reviewed tests are failing Do not merge until tests pass labels May 18, 2026

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Click here to look at the relevant links ⬇️

🔗 Relevant Links

Repository:

Python:

Automated review generated by algorithms-keeper. If there's any problem regarding this review, please open an issue about it.

algorithms-keeper commands and options

algorithms-keeper actions can be triggered by commenting on this PR:

  • @algorithms-keeper review to trigger the checks for only added pull request files
  • @algorithms-keeper review-all to trigger the checks for all the pull request files, including the modified files. As we cannot post review comments on lines not part of the diff, this command will post all the messages in one comment.

NOTE: Commands are in beta and so this feature is restricted only to a member or owner of the organization.

Comment thread maths/lu_decomposition.py
"""


Matrix = list[list[float]]

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Variable and function names should follow the snake_case naming convention. Please update the following name accordingly: Matrix

Comment thread maths/lu_decomposition.py


def solve_with_lu(
lower: list[list[float]], upper: list[list[float]], b: list[float]

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Please provide descriptive name for the parameter: b

@algorithms-keeper algorithms-keeper Bot removed the tests are failing Do not merge until tests pass label May 19, 2026

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Click here to look at the relevant links ⬇️

🔗 Relevant Links

Repository:

Python:

Automated review generated by algorithms-keeper. If there's any problem regarding this review, please open an issue about it.

algorithms-keeper commands and options

algorithms-keeper actions can be triggered by commenting on this PR:

  • @algorithms-keeper review to trigger the checks for only added pull request files
  • @algorithms-keeper review-all to trigger the checks for all the pull request files, including the modified files. As we cannot post review comments on lines not part of the diff, this command will post all the messages in one comment.

NOTE: Commands are in beta and so this feature is restricted only to a member or owner of the organization.

Comment thread maths/lu_decomposition.py
Reference: https://en.wikipedia.org/wiki/LU_decomposition
"""

Matrix = list[list[float]]

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Variable and function names should follow the snake_case naming convention. Please update the following name accordingly: Matrix

Comment thread maths/lu_decomposition.py


def solve_with_lu(
lower: list[list[float]], upper: list[list[float]], b: list[float]

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Please provide descriptive name for the parameter: b

@MD-Mushfiqur123

MD-Mushfiqur123 commented May 19, 2026 via email

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@MD-Mushfiqur123

MD-Mushfiqur123 commented May 19, 2026 via email

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Author

Signed-off-by: god032396-del <god032396@gmail.com>
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