Rectangular matrices

Class: Matrix

2D matrix of real elements. Data format: 
number_of_rows number_of_columns
For each row (i):
   For each column (j):
      elementi,j

Class: Matrix_fixed_dimension

2D matrix of real elements, dimensions are defined in the program and are not specified in the input or output. The documentation for the software should define the numbers of rows and columns. Data format: 
For each row (i):
   For each column (j):
      elementi,j

Class: Matrix2d

2x2 matrix of real elements. and columns. Data format: 
For each row (i):
   For each column (j):
      elementi,j

Class: Matrix3d

3x3 matrix of real elements. and columns. Data format: 
For each row (i):
   For each column (j):
      elementi,j

Class: Matrix4d

4x4 matrix of real elements. and columns. Data format: 
For each row (i):
   For each column (j):
      elementi,j