class_docstr: Construct a mass matrix in various formats of Mikota pair.
  
  The mass matrix `M` is square real diagonal
  positive definite with entries that are reciprocal to integers.
  
  Parameters
  ----------
  shape : tuple of int
      The shape of the matrix.
  dtype : dtype
      Numerical type of the array. Default is ``np.float64``.
  
  Methods
  -------
  toarray()
      Construct a dense array from Mikota data
  tosparse()
      Construct a sparse array from Mikota data
  tobanded()
      The format for banded symmetric matrices,
      i.e., (1, n) ndarray with the main diagonal.
code: def _diag(self):
      # The matrix is constructed from its diagonal 1 / [1, ..., N+1];
      # compute in a function to avoid duplicated code & storage footprint
      return (1.0 / np.arange(1, self.shape[0] + 1)).astype(self.dtype)
  
imports: import numpy
  from scipy.sparse.linalg import LinearOperator
  from scipy.sparse import kron, eye, dia_array
label_desc: Use image node_id 2 for calling the MikotaM obj's underlying member method code with example usage: obj._diag() and returns: unknown