'Sort the indices of this matrix *in place*'

def sort_indices(self):

    if self.has_sorted_indices:
        return
    (R, C) = self.blocksize
    (M, N) = self.shape
    bsr_sort_indices((M // R), (N // C), R, C, self.indptr, self.indices, self.data.ravel())
    self.has_sorted_indices = True
