class_docstr: Simple matrix data type.
  
  Of course there are much more advanced matrix data types for Python (for
  instance, the C{ndarray} data type of Numeric Python) and this implementation
  does not want to compete with them. The only role of this data type is to
  provide a convenient interface for the matrices returned by the C{Graph}
  object (for instance, allow indexing with tuples in the case of adjacency
  matrices and so on).
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docstr: In-place subtraction of a matrix or scalar.
code: def __isub__(self, other):
      """In-place subtraction of a matrix or scalar."""
      if isinstance(other, Matrix):
          if self.shape != other.shape:
              raise ValueError("matrix shapes do not match")
          for row_a, row_b in zip(self._data, other):
              for i in range(len(row_a)):
                  row_a[i] -= row_b[i]
      else:
          for row in self._data:
              for i in range(len(row)):
                  row[i] -= other
      return self
  
label_desc: Use image node_id 13 for calling the Matrix obj's underlying member method code with example usage: obj.__isub__(other) and returns: self