Symbolic lower triangle.
Syntax
tril(X)
tril(X,K)
Description
tril(X) is the lower triangular part of X.
tril(X,K) returns a lower triangular matrix that retains the elements of X on and below the k-th diagonal and sets the remaining elements to 0. The values k=0, k>0, and k<0 correspond to the main, superdiagonals, and subdiagonals, respectively.
Examples
Suppose
A =
[ a, b, c ]
[ 1, 2, 3 ]
[ a+1, b+2, c+3 ]
Then tril(A) returns
[ a, 0, 0 ]
[ 1, 2, 0 ]
[ a+1, b+2, c+3 ]
tril(A,1) returns
[ a, b, 0 ]
[ 1, 2, 3 ]
[ a+1, b+2, c+3 ]
triu(A,-1) returns
[ 0, 0, 0 ]
[ 1, 0, 0 ]
[ a+1, b+2, 0 ]
See Also
diag, triu
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