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diag

  

extract the diagonals from a matrix or create a diagonal matrix

 

Calling Sequence

Parameters

Description

Examples

Calling Sequence

diag(A)

diag(A, k)

Parameters

A

-

matrix, vector, array, or scalar

k

-

(optional) integer

Description

• 

The diag command either creates a matrix with entries on the diagonal, or extracts the entries from the diagonal of a matrix.

• 

The diag(A) command returns a matrix with the entries of A along the main diagonal, and 0 everywhere else when A is a vector, or a matrix with one row or column.

• 

The diag(A, k) command returns a matrix with the entries of A along the kth diagonal specified by the selection parameter k, and 0 everywhere else, when A is a vector, or a matrix with one row or column.

• 

For a matrix A with more than one row and more than one column, the diag(A) command returns the main diagonal of A as a (column) vector.

• 

For a matrix A with more than one row and more than one column, the diag(A, k) command returns the (column) vector corresponding to the diagonal of A, specified by the selection parameter k.

• 

The diagonals of a matrix are indexed using signed integers, where the main diagonal has index 0. Superdiagonals are indexed with positive integers and subdiagonals are indexed with negative integers.

Examples

withMTM:

AMatrix1,2,1,4,5,6,2,8,1

A121456281

(1)

diagA

151

(2)

diagA,1

26

(3)

diagA,1

48

(4)

BVector4,5,6

B456

(5)

diagB

400050006

(6)

diagB,1

0400005000060000

(7)

diagB,1

0000400005000060

(8)

See Also

ArrayTools[Diagonal]

LinearAlgebra[Diagonal]

LinearAlgebra[DiagonalMatrix]

MTM[tril]

MTM[triu]