arrays the components in tuple in the order listed within the brackets and passes the tuple to the ndxtuple argument of the getitem method the contents of the ndxtuple are used to extract the contents of the given element after verifying both subscripts are within the valid rangewe extractfrom the data field therowsthe reference to the array used to store the given row with this reference stored in the local variable the darraywe can then apply the subscript operator to the - array using the column value you may notice second assert statement within the getitem method at line this is needed because python does not examine the number of components specified in the subscript before passing the tuple to the subscript operator method for examplethere is nothing to prevent us from incorrectly supplying three components such as box[ , ,kinstead of two in factpython would have no way of knowing that we only need two components for the - array subscript thuswe must first check to make sure the subscript tuple passed to the method contains only two elements when making the assertion about the size of the ndxtuplewe assume tuple is passed to the subscript operator and use the len(function to verify its length when single-component subscript [ is supplied to subscript operator methodas is done with the array classthe argument is single integer value the len(method can only be used with the collection types and not individual values it does generate its own errorhoweverwhen used improperly thuspython' len(function is used to ensure two components are supplied for all array objects the setitem operator method can be implemented in similar fashion to getitem the major differences are that this method requires second argument to receive the value to which an element is set and it modifies the indicated element with the new value instead of returning value the matrix abstract data type in mathematicsa matrix is an rectangular grid or table of numerical values divided into rows and columns matriceswhich are an important tool in areas such as linear algebra and computer graphicsare used in number of applicationsincluding representing and solving systems of linear equations the matrix adt is defined next define matrix adt matrix is collection of scalar values arranged in rows and columns as rectangular grid of fixed size the elements of the matrix can be accessed by specifying given row and column index with indices starting at matrixrowsncols )creates new matrix containing nrows and ncols with each element initialized to numrows()returns the number of rows in the matrix