# Global Functions¶

This section lists functions that are specific to the active data types and tape management. For mathematical functions, Mathematical Operations.

`value`

¶

`value(T& x)`

returns a reference (or const-reference if `x`

is constant) to the value stored in `x`

.

If `x`

is a XAD active data type, such as `AReal`

or `FReal`

, this function returns a reference to the stored value (which is assignable).

If `x`

is a passive data type, this function simple returns the value itself.

This function is especially useful in generic code, as it is defined on any data type.

`derivative`

¶

`derivative(const T& x)`

returns a reference (or const-reference if `x`

is constant) to the derivative stored in `x`

.

If `x`

is a XAD active data type, such as `AReal`

or `FReal`

, this function returns a reference to the stored derivative (which is assignable).

If `x`

is a passive data type, this function simply returns 0.

This function is especially useful in generic code, as it is defined on any data type.