# tril

Lower triangular part of a matrix

### tril(X)

• X should be a matrix, i.e., ndims(X) equal to 2.
• It returns the lower triangular part of X, i.e., elements below and on the main diagonal of X.
• If X is a character array, elements above the main diagonal are filled with the white-space character.
• It returns an empty matrix if X is empty.

### tril(X, k)

• k should be an integer scalar, not equal to NaN or Inf.
• If k < 0, it returns elements below and on the lower k-th diagonal of X.
• If k > 0, it returns elements below and on the upper k-th diagonal of X.
• If k == 0, it returns the same result as tril(X).

Example 1: In the following, tril() extracts the lower triangular part of a character array. The upper part is filled with spaces.

a=['abcd';'efgh';'ijkl';'mnop']
tril(a)

a =
abcd
efgh
ijkl
mnop

ans =
a
ef
ijk
mnop