linalg:triu

(linalg:triu array &key k)

Returns the upper triangle of array: a copy with everything below the k-th diagonal set to zero (numpy's np.triu). :k defaults to 0, which keeps the main diagonal; a positive :k moves the boundary up and to the right, a negative one down and to the left. Rank must be at least 2, and for a stack of matrices the last two axes are the matrix. Applied to an all-ones matrix with :k 1 this is the causal ("subsequent") attention mask. The mirror is linalg:tril.