Cholesky Decomposition Calculator

Decompose a symmetric positive-definite matrix into A = LLᵀ with animated step-by-step computation. See each element of the lower-triangular matrix L derived with full formulas, verify the result, and explore the factorization visually.

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About Cholesky Decomposition Calculator

The Cholesky Decomposition Calculator factors a symmetric positive-definite matrix A into the product of a lower-triangular matrix L and its transpose Lᵀ, so that A = LLᵀ. This factorization is fundamental in numerical linear algebra, offering roughly twice the efficiency of general LU decomposition by exploiting the symmetry and positive-definiteness of the input matrix. The calculator provides animated step-by-step derivations, interactive cell highlighting, and automatic verification that LLᵀ reconstructs A.

How Cholesky Decomposition Works

Given an n×n symmetric positive-definite matrix A, the algorithm computes L column by column. For each column j:

Diagonal element:

$$L_{jj} = \sqrt{A_{jj} - \sum_{k=1}^{j-1} L_{jk}^2}$$

Off-diagonal elements (for i > j):

$$L_{ij} = \frac{1}{L_{jj}} \left( A_{ij} - \sum_{k=1}^{j-1} L_{ik} L_{jk} \right)$$

The algorithm proceeds left to right across columns. Each diagonal element involves a square root, which is guaranteed to be real and positive when A is positive-definite. If a negative value appears under the square root, the matrix is not positive-definite.

Conditions for Cholesky Decomposition

Condition	Requirement	What Happens If Violated
Symmetric	A = Aᵀ (A[i,j] = A[j,i])	Decomposition is undefined
Positive-Definite	All eigenvalues > 0	Negative under square root
Square	n×n matrix	Not applicable to rectangular

Key Properties

▽

Lower-Triangular

L has zeros above the diagonal

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Unique

If A is positive-definite, L is unique

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Efficient

~n³/3 operations vs n³/3 × 2 for LU

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Stable

No pivoting needed — always stable

↔

det(A) = det(L)²

Determinant from diagonal of L

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Solving Ax = b

Forward then back substitution

How to Use the Cholesky Decomposition Calculator

Select matrix size — Choose from 2×2 up to 6×6. Cholesky decomposition requires a square matrix.
Enter values — Fill in the matrix cells. The calculator auto-mirrors entries across the diagonal to enforce symmetry (editing A[i,j] automatically sets A[j,i]).
Click Decompose — Press the "Decompose A = LLᵀ" button to compute the factorization.
Explore the result — Review the color-coded equation A = L × Lᵀ. Click any cell in L to see its derivation formula. Use "Play All" to auto-step through every element.
Verify — The calculator multiplies L × Lᵀ back together and reports the maximum error, confirming the decomposition is correct.

Real-World Applications

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Monte Carlo

Generate correlated random variables from a covariance matrix

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Kalman Filters

State estimation in navigation and signal processing

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Machine Learning

Gaussian processes, covariance inversion

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Optimization

Newton's method with positive-definite Hessians

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Finance

Portfolio risk modeling via correlation decomposition

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Engineering

Finite element method stiffness matrices

Cholesky vs Other Decompositions

Method	Factorization	Requirements	Complexity
Cholesky	A = LLᵀ	Symmetric positive-definite	n³/3
LU	A = LU (or PA = LU)	Invertible	2n³/3
QR	A = QR	Any matrix	2n³/3 (Householder)
SVD	A = UΣVᵀ	Any matrix	~11n³/3
Eigendecomposition	A = QΛQᵀ	Symmetric	~9n³

Frequently Asked Questions

What is Cholesky decomposition?

Cholesky decomposition (named after Andre-Louis Cholesky) factors a symmetric positive-definite matrix A into A = LLᵀ, where L is a lower-triangular matrix with positive diagonal entries. It is one of the most efficient and numerically stable matrix factorizations available.

When can Cholesky decomposition be applied?

The matrix must be symmetric (A = Aᵀ) and positive-definite (all eigenvalues strictly positive, or equivalently, xᵀAx > 0 for every nonzero vector x). Common examples include covariance matrices, correlation matrices, Gram matrices (XᵀX for full-rank X), and stiffness matrices in structural engineering.

What if my matrix is not positive-definite?

If the matrix is not positive-definite, you will encounter a negative value under a square root during the decomposition, which is not a real number. The calculator will report an error indicating exactly which diagonal step failed. You may want to check your matrix for symmetry errors, or consider LDLᵀ decomposition for positive semi-definite matrices.

How is Cholesky decomposition used to solve linear systems?

To solve Ax = b, first decompose A = LLᵀ. Then solve Ly = b by forward substitution (since L is lower-triangular), and then solve Lᵀx = y by back substitution. This is about twice as fast as solving via LU decomposition because L and Lᵀ share the same data.

What is the relationship between Cholesky and the determinant?

Since A = LLᵀ, we have det(A) = det(L) × det(Lᵀ) = det(L)². And since L is triangular, det(L) is simply the product of its diagonal entries. This provides an efficient way to compute the determinant of a positive-definite matrix.

Can Cholesky decomposition be applied to complex matrices?

Yes, for complex matrices the condition is that A must be Hermitian positive-definite (A = A*, where A* is the conjugate transpose). The decomposition becomes A = LLᵀ where Lᵀ is replaced by L* (the conjugate transpose of L). This calculator handles real-valued matrices.

Reference this content, page, or tool as:

"Cholesky Decomposition Calculator" at https://MiniWebtool.com/cholesky-decomposition-calculator/ from MiniWebtool, https://MiniWebtool.com/

by miniwebtool team. Updated: 2026-04-12

Developer API available: Run this tool from your app, automation, or agent with one JSON HTTP request. View API docs

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