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Upper triangular matrix
By rohit.pandey1
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Updated on 17 Apr 2025, 18:05 IST
An upper triangular matrix is a cornerstone concept in linear algebra, essential for solving systems of equations, matrix decompositions, and eigenvalue problems.
What is an Upper Triangular Matrix?
Definition:
An upper triangular matrix is a square matrix where all elements below the principal diagonal are zero. For a matrix U=[Uij] of order n×n:
uij=0for alli>j.
Here, ii is the row index, and jj is the column index.
Example of a 3x3 Upper Triangular Matrix:
All elements below the diagonal (positions (2,1),(3,1),(3,2)(2,1),(3,1),(3,2)) are zero.
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In Hindi (त्रिकोणीय आव्यूह):
एक ऊपरी त्रिकोणीय आव्यूह वह वर्ग आव्यूह है जिसमें मुख्य विकर्ण के नीचे के सभी अवयव शून्य होते हैं। उदाहरण:
Types of Upper Triangular Matrices
- Strictly Upper Triangular Matrix:
- All diagonal and below-diagonal elements are zero.
Example:
- Diagonal elements are 11, with zeros below.
Example:
Key Properties
Determinant:
The determinant is the product of diagonal elements:
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Eigenvalues:
The eigenvalues of an upper triangular matrix are its diagonal entries.
- Sum/Product: Sum or product of two upper triangular matrices is upper triangular.
- Inverse: If invertible (diagonal entries ≠ 0), the inverse is upper triangular.
- Transpose: Transpose of an upper triangular matrix is a lower triangular matrix.
Examples of Upper Triangular Matrices
3x3 Upper Triangular Matrix:
Determinant: 1×5×9=451×5×9=45.
4x4 Upper Triangular Matrix:
Determinant: 2×7×6×4=3362×7×6×4=336.
Applications
- Solving Linear Systems:
Used in Gaussian elimination to simplify systems like Ux=bUx=b. - Matrix Decompositions:
Key in LU decomposition, where a matrix is split into lower (L) and upper (U) triangular matrices. - Eigenvalue Computations:
Simplifies eigenvalue problems in algorithms like the QR algorithm. - Computer Graphics:
Represents geometric transformations like scaling and shearing.
How to Convert a Matrix to Upper Triangular Form
Example: Convert A=[123456789]A=147258369:
- Step 1: Subtract 4×Row 14×Row 1 from Row 2.
- Step 2: Subtract 7×Row 17×Row 1 from Row 3.
- Step 3: Subtract 2×Row 22×Row 2 from Row 3.
Result:
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FAQs: Upper Triangular Matrix
What is the definition of an upper triangular matrix?
An upper triangular matrix is a square matrix in which all the elements below the main (principal) diagonal are zero.
Can you give an upper triangular matrix example?
Yes, for example,
is an upper triangular matrix.
What is the upper triangular matrix meaning in simple terms?
It means only the elements on or above the main diagonal can be non-zero; everything below must be zero.
What is a strictly upper triangular matrix?
A strictly upper triangular matrix is one where all the diagonal and below-diagonal elements are zero; only elements above the diagonal may be non-zero.
What is a unit upper triangular matrix?
It is an upper triangular matrix where all the diagonal elements are 1, and all elements below the diagonal are zero.
How do you find the determinant of an upper triangular matrix?
The determinant is the product of the diagonal elements of the matrix.
What are the eigenvalues of an upper triangular matrix?
The eigenvalues are the entries on the main diagonal of the matrix.
What happens when you add or multiply two upper triangular matrices?
The sum or product of two upper triangular matrices is also an upper triangular matrix.
What is the transpose of an upper triangular matrix?
The transpose of an upper triangular matrix is a lower triangular matrix.
Where are upper triangular matrices used in real life?
They are used in solving linear equations (Gaussian elimination), LU decomposition, computer graphics, data science, engineering, finance, and physics for simplifying calculations and models.