UpperTriangularize

gives a matrix in which all but the upper triangular elements of m are replaced with zeros.

replaces with zeros only the elements below the k subdiagonal of m.

Details

UpperTriangularize[m] works even if m is not a square matrix.
In UpperTriangularize[m,k], positive k refers to subdiagonals above the main diagonal and negative k refers to subdiagonals below the main diagonal.
UpperTriangularize works with SparseArray objects.

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Get the upper triangular part of a matrix:

Get the strictly upper triangular part of a matrix:

Get the upper triangular part of nonsquare matrices:

The number of rows or columns limits the meaningful values of the parameter k:

Introduced in 2008

(7.0)

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