Eigen
3.3.4

Generic expression of a matrix where all coefficients are defined by a functor.
NullaryOp  template functor implementing the operator 
PlainObjectType  the underlying plain matrix/array type 
This class represents an expression of a generic nullary operator. It is the return type of the Ones(), Zero(), Constant(), Identity() and Random() methods, and most of the time this is the only way it is used.
However, if you want to write a function returning such an expression, you will need to use this class.
The functor NullaryOp must expose one of the following method:
operator()()  if the procedural generation does not depend on the coefficient entries (e.g., random numbers) 
operator()(Index i)  if the procedural generation makes sense for vectors only and that it depends on the coefficient index i (e.g., linspace) 
operator()(Index i,Index j)  if the procedural generation depends on the matrix coordinates i , j (e.g., to generate a checkerboard with 0 and 1) 
It is also possible to expose the last two operators if the generation makes sense for matrices but can be optimized for vectors.
See DenseBase::NullaryExpr(Index,const CustomNullaryOp&) for an example binding C++11 random number generators.
A nullary expression can also be used to implement custom sophisticated matrix manipulations that cannot be covered by the existing set of natively supported matrix manipulations. See this page for some examples and additional explanations on the behavior of CwiseNullaryOp.
Inherits type< CwiseNullaryOp< NullaryOp, PlainObjectType > >, and Eigen::internal::no_assignment_operator.
Public Member Functions  
const NullaryOp &  functor () const 

inline 