input: Write a function to filter out all negative numbers from a given matrix and return the modified matrix where all negative numbers are set to 0. Assume the matrix is provided as a list of lists.
  assert filter_out_negative([[-1, 2, -3], [-4, 5, 6], [-7, 8, 9]])==np.array([[0, 2, 0], [0, 5, 6], [0, 8, 9]])
output: def filter_out_negative(matrix):
      return [[0 if x < 0 else x for x in row] for row in matrix]