NAME

       eye - the identity matrix

DESCRIPTION

       Following matlab, the name eye() is used in place of I to denote identity matrices because
       I is often used as a subscript or as sqrt(-1). The dimensions of eye() are  determined  by
       context.   The  preconditioner  interface  is  usefull when calling algorithms without any
       preconditioners, e.g.

           int status = pcg (a, x, b, eye(), 100, 1e-7);

IMPLEMENTATION

       class eye {
       public:
         eye() {}
         template<class T> const vec<T>& operator* (const vec<T>& x) const { return x; }
         template<class T> const vec<T>& solve (const vec<T>& x) const { return x; }
         template<class T> const vec<T>& trans_solve (const vec<T>& x) const { x; }
       };