Expression of a coefficient wise version of the C++ ternary operator ?:
| ConditionMatrixType | the type of the condition expression which must be a boolean matrix | 
| ThenMatrixType | the type of the then expression | 
| ElseMatrixType | the type of the else expression | 
This class represents an expression of a coefficient wise version of the C++ ternary operator ?:. It is the return type of DenseBase::select() and most of the time this is the only way it is used.
Inherits internal::dense_xpr_base::type, and Eigen::internal::no_assignment_operator.
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