Class TRBDF2

See http://ssrn.com/abstract=1648878 for details.

In this implementation, the passed operator must be derived from either TimeConstantOperator or TimeDependentOperator. Also, it must implement at least the following interface:

typedef ... array_type;

// copy constructor/assignment
// (these will be provided by the compiler if none is defined)
Operator(const Operator&);
Operator& operator=(const Operator&);

// inspectors
Size size();

// modifiers
void setTime(Time t);

// operator interface
array_type applyTo(const array_type&);
array_type solveFor(const array_type&);
static Operator identity(Size size);

// operator algebra
Operator operator*(Real, const Operator&);
Operator operator+(const Operator&, const Operator&);
Operator operator+(const Operator&, const Operator&);

warning The differential operator must be linear for this evolver to work.

NOTE: There is room for performance improvement especially in the array manipulation