code: def triu(A, k=0, format=None):
      """Return the upper triangular portion of a matrix in sparse format
  
      Returns the elements on or above the k-th diagonal of the matrix A.
          - k = 0 corresponds to the main diagonal
          - k > 0 is above the main diagonal
          - k < 0 is below the main diagonal
  
      Parameters
      ----------
      A : dense or sparse matrix
          Matrix whose upper trianglar portion is desired.
      k : integer : optional
          The bottom-most diagonal of the upper triangle.
      format : string
          Sparse format of the result, e.g. format="csr", etc.
  
      Returns
      -------
      L : sparse matrix
          Upper triangular portion of A in sparse format.
  
      See Also
      --------
      tril : lower triangle in sparse format
  
      Examples
      --------
      >>> from scipy.sparse import csr_matrix, triu
      >>> A = csr_matrix([[1, 2, 0, 0, 3], [4, 5, 0, 6, 7], [0, 0, 8, 9, 0]],
      ...                dtype='int32')
      >>> A.toarray()
      array([[1, 2, 0, 0, 3],
             [4, 5, 0, 6, 7],
             [0, 0, 8, 9, 0]])
      >>> triu(A).toarray()
      array([[1, 2, 0, 0, 3],
             [0, 5, 0, 6, 7],
             [0, 0, 8, 9, 0]])
      >>> triu(A).nnz
      8
      >>> triu(A, k=1).toarray()
      array([[0, 2, 0, 0, 3],
             [0, 0, 0, 6, 7],
             [0, 0, 0, 9, 0]])
      >>> triu(A, k=-1).toarray()
      array([[1, 2, 0, 0, 3],
             [4, 5, 0, 6, 7],
             [0, 0, 8, 9, 0]])
      >>> triu(A, format='csc')
      <3x5 sparse matrix of type '<class 'numpy.int32'>'
              with 8 stored elements in Compressed Sparse Column format>
  
      """
  
      # convert to COOrdinate format where things are easy
      A = coo_matrix(A, copy=False)
      mask = A.row + k <= A.col
      return _masked_coo(A, mask).asformat(format)
  
imports: from .coo import coo_matrix
label_desc: Use image node_id 3 for calling a global function with example usage: triu(A, k, format) and returns: _masked_coo