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单词 TriangularMatrix
释义

triangular matrix


1 Triangular Matrix

Let n be a positive integer.

An upper triangular matrixMathworldPlanetmath is of the form:

[a11a12a13a1n0a22a23a2n00a33a3n000ann]

An upper triangular matrix is sometimes also called right triangular.

A lower triangular matrix is of the form:

[a11000a21a2200a31a32a330an1an2an3ann]

A lower triangular matrix is sometimes also called left triangular.

Note that upper triangular matrices and lower triangular matrices must be square matricesMathworldPlanetmath.

A triangular matrix is a matrix that is an upper triangular matrix or lower triangular matrix. Note that some matrices, such as the identity matrixMathworldPlanetmath, are both upper and lower triangular. A matrix is upper and lower triangular simultaneously if and only if it is a diagonal matrixMathworldPlanetmath.

Triangular matrices allow numerous algorithmic shortcuts in many situations. For example, if A is an n×n triangular matrix, the equation Ax=b can be solved for x in at most n2 operations.

In fact, triangular matrices are so useful that much computational linear algebra begins with factoring (or decomposing) a general matrix or matrices into triangular form. Some matrix factorization methods are the Cholesky factorization and the LU-factorization. Even including the factorization step, enough later operations are typically avoided to yield an overall time savings.

2 Properties

Triangular matrices have the following properties ( “triangular” with either “upper” or “lower” uniformly):

  • The inversePlanetmathPlanetmath of a triangular matrix is a triangular matrix.

  • The product of two triangular matrices is a triangular matrix.

  • The determinantMathworldPlanetmath of a triangular matrix is the product of the diagonal elements.

  • The eigenvaluesMathworldPlanetmathPlanetmathPlanetmathPlanetmath of a triangular matrix are the diagonal elements.

The last two properties follow easily from the cofactor expansion of the triangular matrix.

Titletriangular matrix
Canonical nameTriangularMatrix
Date of creation2013-03-22 12:11:40
Last modified on2013-03-22 12:11:40
OwnerWkbj79 (1863)
Last modified byWkbj79 (1863)
Numerical id13
AuthorWkbj79 (1863)
Entry typeDefinition
Classificationmsc 65-00
Classificationmsc 15-00
Definesupper triangular
Defineslower triangular
Definesupper triangular matrix
Defineslower triangular matrix
Definesright triangular
Definesright triangular matrix
Definesleft triangular
Definesleft triangular matrix
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