template<typename T>
NumTraits class
Holds information about the various numeric (i.e. scalar) types allowed by Eigen.
Template parameters | |
---|---|
T | the numeric type at hand |
This class stores enums, typedefs and static methods giving information about a numeric type.
The provided data consists of:
- A typedef
Real
, giving the "real part" type of T. If T is already real, thenReal
is just a typedef to T. If T isstd::complex<U>
thenReal
is a typedef to U. - A typedef
NonInteger
, giving the type that should be used for operations producing non-integral values, such as quotients, square roots, etc. If T is a floating-point type, then this typedef just gives T again. Note however that many Eigen functions such as internal::sqrt simply refuse to take integers. Outside of a few cases, Eigen doesn't do automatic type promotion. Thus, this typedef is only intended as a helper for code that needs to explicitly promote types. - A typedef
Literal
giving the type to use for numeric literals such as "2" or "0.5". For instance, forstd::complex<U>
, Literal is defined asU
. Of course, this type must be fully compatible with T. In doubt, just use T here. - A typedef Nested giving the type to use to nest a value inside of the expression tree. If you don't know what this means, just use T here.
- An enum value IsComplex. It is equal to 1 if T is a
std::complex
type, and to 0 otherwise. - An enum value IsInteger. It is equal to
1
if T is an integer type such asint
, and to0
otherwise. - Enum values ReadCost, AddCost and MulCost representing a rough estimate of the number of CPU cycles needed to by move / add / mul instructions respectively, assuming the data is already stored in CPU registers. Stay vague here. No need to do architecture-specific stuff. If you don't know what this means, just use
Eigen::
.HugeCost - An enum value IsSigned. It is equal to
1
if T is a signed type and to 0 if T is unsigned. - An enum value RequireInitialization. It is equal to
1
if the constructor of the numeric type T must be called, and to 0 if it is safe not to call it. Default is 0 if T is an arithmetic type, and 1 otherwise. - An epsilon() function which, unlike std::
numeric_limits:: epsilon(), it returns a Real instead of a T. - A dummy_precision() function returning a weak epsilon value. It is mainly used as a default value by the fuzzy comparison operators.
- highest() and lowest() functions returning the highest and lowest possible values respectively.
- digits10() function returning the number of decimal digits that can be represented without change. This is the analogue of std::
numeric_limits<T>:: digits10 which is used as the default implementation if specialized.